Methods and systems for engine cranking

ABSTRACT

Systems and methods for improving operation of a hybrid vehicle are presented. In one example, an engine may be started in one of two ways depending on operating conditions. In particular, the engine may be started via a lower power output electric machine or a higher power output electric machine.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication 61/643,173 filed on May 4, 2012, the entire contents ofwhich are hereby incorporated by reference for all purposes.

FIELD

The present description relates to a system and methods for improvingdrivability and fuel economy of a vehicle. The methods may beparticularly useful for engines that are selectively coupled to anelectrical machine and a transmission.

BACKGROUND AND SUMMARY

Hybrid vehicles may include and engine and an electric machine to propelthe vehicle. In some vehicle designs, the engine may have significantlyhigher output capacity than the electric machine due to packaging andweight constraints. The electric machine may be used to start the engineand to provide a small amount of torque to launch a vehicle in which theengine and electric machine reside. However, the electric machine maynot be useful to accelerate beyond vehicle creep speed withoutassistance from the engine since the electric machine is tasked withaccelerating the vehicle and starting the engine. Consequently, theelectric machine may provide limited use beyond starting the engine.

The inventors herein have recognized the above-mentioned disadvantagesand have developed a method of starting an engine, comprising: during afirst condition, starting an engine with a first electrical machinewhile a driveline disconnect clutch is closed; and during a secondcondition, starting the engine with a second electrical machine whilethe driveline disconnect clutch is open.

In other words, the engine may be started by two electric machinesduring different conditions so that one electric machine may help toprovide torque to a vehicle driveline over a broader range of conditionswhile the other electric machine may have a specific function ofstarting the engine. For example, a driveline integratedstarter/generator may start the engine and provide torque to a drivelineduring low driver demand torque conditions. Further, the drivelineintegrated starter/generator may supply torque to the driveline athigher drive demand torque conditions while a lower power outputcapacity electric machine starts the engine. The lower power capacityelectric machine allows the driveline integrated starter/generator toprovide driveline torque over a broader driver demand torque range. Inthis way, a smaller driveline integrated starter/generator may provide adriveline torque function that heretofore required a larger electricmachine.

The present description may provide several advantages. Specifically,the approach may extend a driver demand torque range of a drivelineintegrated starter/generator. Further, the approach may improve enginestarting by allowing the engine to accelerate to a speed of thedriveline integrated starter/generator before a driveline disconnectclutch is closed.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings, where:

FIG. 1 is a schematic diagram of an engine;

FIG. 2 is shows a first example vehicle driveline configuration;

FIG. 3 is shows a second example vehicle driveline configuration;

FIG. 4 is a flowchart showing one example of operating a vehicledriveline with the methods described in the subsequent figures;

FIGS. 5-8 show flowcharts and conditions for operating a hybrid vehiclepowertrain in response to driving route conditions;

FIGS. 9 and 10 show a method and prophetic sequence for adjustingpowertrain operation in response to vehicle mass;

FIGS. 11 and 12 show a method and prophetic sequence for starting ahybrid vehicle;

FIGS. 13 and 14 show a method and prophetic sequence for adjusting fuelto a hybrid powertrain during engine starting;

FIGS. 15-18 show methods and prophetic sequences for starting an engineof a hybrid vehicle during transmission shifting;

FIGS. 19-22 show methods and prophetic sequences for providing flywheeland driveline disconnect clutch compensation;

FIGS. 23-26 show methods and prophetic sequences for stopping an engineof a hybrid vehicle;

FIGS. 27 and 28 show a method and prophetic sequence for holding ahybrid vehicle with a stopped engine on a hill;

FIGS. 29A-36 show methods and prophetic sequences for operating a hybridpowertrain with driveline braking;

FIGS. 37-40 show methods and prophetic sequences for operating a hybridpowertrain in a sailing mode;

FIGS. 41-44 show methods and prophetic sequences for adapting drivelinedisconnect clutch operation; and

FIGS. 45-48 show prophetic functions for describing or modeling atransmission torque converter.

DETAILED DESCRIPTION

The present description is related to controlling a driveline of ahybrid vehicle. The hybrid vehicle may include an engine and electricmachine as shown in FIGS. 1-3. The engine may be operated with orwithout a driveline integrated starter/generator (e.g., an electricmachine or motor that may be abbreviated DISG) during vehicle operation.The driveline integrated starter/generator is integrated into thedriveline on the same axis as the engine crankshaft and rotates wheneverthe torque converter impeller rotates. Further, the DISG may not beselectively engaged or disengaged with the driveline. Rather, the DISGis an integral part of the driveline. Further still, the DISG may beoperated with or without operating the engine. The mass and inertia ofthe DISG remain with the driveline when the DISG is not operating toprovide or absorb torque from the driveline.

The driveline may be operated according to the method of FIG. 4. In someexamples, the driveline may be operated based on a driving route andvehicle mass as described in FIGS. 5-10. The engine may be startedaccording to the methods shown in FIGS. 11 through 18. Drivelinecomponent compensation may be provided as described in FIGS. 19-22. Fuelmay be conserved by selectively stopping the engine as described inFIGS. 23-28. The driveline may also enter a regeneration mode asdescribed in FIGS. 29A-36 where the vehicle's kinetic energy isconverted in to electrical energy. The electrical energy may besubsequently used to propel the vehicle. During some conditions, thevehicle driveline may enter a sailing mode where the engine is operatedbut not mechanically coupled to the DISG or the transmission or vehiclewheels as described in FIGS. 37-40. Operation of the drivelinedisconnect clutch may be adapted as shown in FIGS. 41 through 44. Themethods described herein may be used together at the same time so as tooperate in a system that performs multiple methods. Finally, FIGS. 45-47show prophetic functions for describing a transmission torque converter.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Flywheel 97 and ring gear 99 arecoupled to crankshaft 40. Starter 96 includes pinion shaft 98 and piniongear 95. Pinion shaft 98 may selectively advance pinion gear 95 toengage ring gear 99. Starter 96 may be directly mounted to the front ofthe engine or the rear of the engine. In some examples, starter 96 mayselectively supply torque to crankshaft 40 via a belt or chain. Starter96 may be described as a lower power starting device. In one example,starter 96 is in a base state when not engaged to the engine crankshaft.Combustion chamber 30 is shown communicating with intake manifold 44 andexhaust manifold 48 via respective intake valve 52 and exhaust valve 54.Each intake and exhaust valve may be operated by an intake cam 51 and anexhaust cam 53. The position of intake cam 51 may be determined byintake cam sensor 55. The position of exhaust cam 53 may be determinedby exhaust cam sensor 57.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector 66delivers liquid fuel in proportion to the pulse width of signal FPW fromcontroller 12. Fuel is delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, fuel pump, and fuel rail (not shown).Fuel injector 66 is supplied operating current from driver 68 whichresponds to controller 12. In addition, intake manifold 44 is showncommunicating with optional electronic throttle 62 which adjusts aposition of throttle plate 64 to control air flow from air intake 42 tointake manifold 44. In one example, a low pressure direct injectionsystem may be used, where fuel pressure can be raised to approximately20-30 bar. Alternatively, a high pressure, dual stage, fuel system maybe used to generate higher fuel pressures. In some examples, throttle 62and throttle plate 64 may be positioned between intake valve 52 andintake manifold 44 such that throttle 62 is a port throttle.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst, aparticulate filter, a lean NOx trap, selective reduction catalyst, orother emissions control device. An emissions device heater 119 may alsobe positioned in the exhaust system to heat converter 70 and/or exhaustgases.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing force and/orposition applied by foot 132; a position sensor 154 coupled to brakepedal 150 for sensing force and/or position applied by foot 152; ameasurement of engine manifold pressure (MAP) from pressure sensor 122coupled to intake manifold 44; an engine position sensor from a Halleffect sensor 118 sensing crankshaft 40 position; a measurement of airmass entering the engine from sensor 120; and a measurement of throttleposition from sensor 58. Barometric pressure may also be sensed (sensornot shown) for processing by controller 12. In a preferred aspect of thepresent description, engine position sensor 118 produces a predeterminednumber of equally spaced pulses every revolution of the crankshaft fromwhich engine speed (RPM) can be determined.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle as shown in FIGS. 2 and 3. Further, in someexamples, other engine configurations may be employed, for example adiesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is shown merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

FIG. 2 is a block diagram of a vehicle driveline 200 in vehicle 290.Driveline 200 may be powered by engine 10. Engine 10 may be started withan engine starting system shown in FIG. 1 or via DISG 240. Further,engine 10 may generate or adjust torque via torque actuator 204, such asa fuel injector, throttle, etc.

An engine output torque may be transmitted to an input side of dual massflywheel 232. Engine speed as well as dual mass flywheel input sideposition and speed may be determined via engine position sensor 118.Dual mass flywheel 232 may include springs and separate masses (notshown) for dampening driveline torque disturbances. The output side ofdual mass flywheel 232 is shown being mechanically coupled to the inputside of driveline disconnect clutch 236. Driveline disconnect clutch 236may be electrically or hydraulically actuated. A position sensor 234 ispositioned on the driveline disconnect clutch side of dual mass flywheel232 to sense the output position and speed of the dual mass flywheel232. In some examples, position sensor 234 may include a torque sensor.The downstream side of driveline disconnect clutch 236 is shownmechanically coupled to DISG input shaft 237.

DISG 240 may be operated to provide torque to driveline 200 or toconvert driveline torque into electrical energy to be stored in electricenergy storage device 275. DISG 240 has a power output that is greaterthan starter 96 shown in FIG. 1. Further, DISG 240 directly drivesdriveline 200 or is directly driven by driveline 200. There are nobelts, gears, or chains to couple DISG 240 to driveline 200. Rather,DISG 240 rotates at the same rate as driveline 200. Electrical energystorage device 275 may be a battery, capacitor, or inductor. Thedownstream side of DISG 240 is mechanically coupled to the impeller 285of torque converter 206 via shaft 241. The upstream side of the DISG 240is mechanically coupled to the driveline disconnect clutch 236.

Torque converter 206 includes a turbine 286 to output torque to inputshaft 270. Input shaft 270 mechanically couples torque converter 206 toautomatic transmission 208. Torque converter 206 also includes a torqueconverter bypass lock-up clutch 212 (TCC). Torque is directlytransferred from impeller 285 to turbine 286 when TCC is locked. TCC iselectrically operated by controller 12. Alternatively, TCC may behydraulically locked. In one example, the torque converter may bereferred to as a component of the transmission. Torque converterimpeller speed and position may be determined via sensor 238. Torqueconverter turbine speed and position may be determined via positionsensor 239. In some examples, 238 and/or 239 may be torque sensors ormay be combination position and torque sensors.

When torque converter clutch 212 is fully disengaged, torque converter206 transmits engine torque to automatic transmission 208 via fluidtransfer between the torque converter turbine 286 and torque converterimpeller 285, thereby enabling torque multiplication. In contrast, whentorque converter clutch 212 is fully engaged, the engine output torqueis directly transferred via the torque converter clutch to an inputshaft 270 of transmission 208. Alternatively, the torque converterclutch 212 may be partially engaged, thereby enabling the amount oftorque directly relayed to the transmission to be adjusted. Thecontroller 12 may be configured to adjust the amount of torquetransmitted by torque converter 206 by adjusting the torque converterclutch 212 in response to various engine operating conditions, or basedon a driver-based engine operation request.

Automatic transmission 208 includes gear clutches (e.g., gears 1-6) 211and forward clutch 210. The gear clutches 211 and the forward clutch 210may be selectively engaged to propel a vehicle. Torque output from theautomatic transmission 208 may in turn be relayed to wheels 216 topropel the vehicle via output shaft 260. Output shaft 260 deliverstorque from transmission 308 to wheels 216 via differential 255 whichincludes first gear 257 and second gear 258. Automatic transmission 208may transfer an input driving torque at the input shaft 270 responsiveto a vehicle traveling condition before transmitting an output drivingtorque to the wheels 216.

Further, a frictional force may be applied to wheels 216 by engagingwheel friction brakes 218. In one example, wheel friction brakes 218 maybe engaged in response to the driver pressing his foot on a brake pedal(not shown). In other examples, controller 12 or a controller linked tocontroller 12 may apply engage wheel friction brakes. In the same way, africtional force may be reduced to wheels 216 by disengaging wheelfriction brakes 218 in response to the driver releasing his foot from abrake pedal. Further, vehicle brakes may apply a frictional force towheels 216 via controller 12 as part of an automated engine stoppingprocedure.

A mechanical oil pump 214 may be in fluid communication with automatictransmission 208 to provide hydraulic pressure to engage variousclutches, such as forward clutch 210, gear clutches 211, and/or torqueconverter clutch 212. Mechanical oil pump 214 may be operated inaccordance with torque converter 206, and may be driven by the rotationof the engine or DISG via input shaft 241, for example. Thus, thehydraulic pressure generated in mechanical oil pump 214 may increase asan engine speed and/or DISG speed increases, and may decrease as anengine speed and/or DISG speed decreases.

Controller 12 may be configured to receive inputs from engine 10, asshown in more detail in FIG. 1, and accordingly control a torque outputof the engine and/or operation of the torque converter, transmission,DISG, clutches, and/or brakes. As one example, an engine torque outputmay be controlled by adjusting a combination of spark timing, fuel pulsewidth, fuel pulse timing, and/or air charge, by controlling throttleopening and/or valve timing, valve lift and boost for turbo- orsuper-charged engines. In the case of a diesel engine, controller 12 maycontrol the engine torque output by controlling a combination of fuelpulse width, fuel pulse timing, and air charge. In all cases, enginecontrol may be performed on a cylinder-by-cylinder basis to control theengine torque output. Controller 12 may also control torque output andelectrical energy production from DISG by adjusting current flowing toand from DISG windings as is known in the art.

When idle-stop conditions are satisfied, controller 12 may initiateengine shutdown by shutting off fuel and spark to the engine. However,the engine may continue to rotate in some examples. Further, to maintainan amount of torsion in the transmission, the controller 12 may groundrotating elements of transmission 208 to a case 259 of the transmissionand thereby to the frame of the vehicle. In particular, the controller12 may engage one or more transmission clutches, such as forward clutch210, and lock the engaged transmission clutch(es) to the transmissioncase 259 and vehicle frame as described in U.S. patent application Ser.No. 12/833,788 “METHOD FOR CONTROLLING AN ENGINE THAT MAY BEAUTOMATICALLY STOPPED” which is hereby fully incorporated by referencefor all intents and purposes. A transmission clutch pressure may bevaried (e.g., increased) to adjust the engagement state of atransmission clutch, and provide a desired amount of transmissiontorsion.

A wheel brake pressure may also be adjusted during the engine shutdown,based on the transmission clutch pressure, to assist in tying up thetransmission while reducing a torque transferred through the wheels.Specifically, by applying the wheel brakes 218 while locking one or moreengaged transmission clutches, opposing forces may be applied ontransmission, and consequently on the driveline, thereby maintaining thetransmission gears in active engagement, and torsional potential energyin the transmission gear-train, without moving the wheels. In oneexample, the wheel brake pressure may be adjusted to coordinate theapplication of the wheel brakes with the locking of the engagedtransmission clutch during the engine shutdown. As such, by adjustingthe wheel brake pressure and the clutch pressure, the amount of torsionretained in the transmission when the engine is shutdown may beadjusted.

When restart conditions are satisfied, and/or a vehicle operator wantsto launch the vehicle, controller 12 may reactivate the engine byresuming combustion in cylinders. As further elaborated with referenceto FIGS. 11-18, the engine may be started in a variety of ways.

Vehicle 290 may also include front 294 and rear 292 windscreen heaters.Windscreen heaters 294 and 292 may be electrically operated and embeddedwithin or coupled to the vehicle's front and rear windscreens 295 and293. Vehicle 290 may also include lights 296, which may or may not bevisible to the driver while the driver is operating vehicle 290. Vehicle290 may also include an electrically operated fuel pump 299 thatsupplies fuel to engine 10 during selected conditions. Finally, vehicle290 may include an electric heater 298 that selectively supplies heat toair in a vehicle cabin or ambient air outside vehicle 290.

Referring now to FIG. 3, a second example vehicle drivelineconfiguration is shown. Many of the elements in driveline 300 aresimilar to the elements of driveline 200 and use equivalent numbers.Therefore, for the sake of brevity, the description of elements that arecommon between FIG. 2 and FIG. 3 is omitted. The description of FIG. 3is limited to elements that are different from the elements of FIG. 2.

Driveline 300 includes a dual clutch—dual layshaft transmission 308.Transmission 308 is essentially an automatically operated manualtransmission. Controller 12 operates first clutch 310, second clutch314, and shifting mechanism 315 to select between gears (e.g.,1^(st)-5^(th) gears) 317. First clutch 310 and second clutch 314 may beselectively opened and closed to shift between gears 317.

The systems of FIG. 1-3 may include torque sensors that may be the basisfor adjusting driveline operation. Alternatively, the torque converteritself may be used as the torque sensor when the torque converter clutch212 is fully disengaged. Specifically, the torque output of an opentorque converter is a function of the input and output speeds, theimpeller and turbine speeds where the impeller in the torque converterinput and the turbine the torque converter output. In the application ofFIGS. 2/3, the impeller speed is equal to the measured DISG speed, asthe DISG rotor output shaft is the impeller input shaft and the turbinespeed is measured and used in the control of the transmission clutchcontrol.

Additionally, given an input and output speed characterization of theopen torque converter, the torque output of the open torque convertercan be controlled by controlling the torque converter impeller speed asa function of the torque converter turbine speed. The DISG may beoperated in speed feedback mode to control torque converter torque. Forexample, the commanded DISG speed (e.g., same as torque converterimpeller speed) is a function of the torque converter turbine speed. Thecommanded DISG speed may be determined as a function of both the DISGspeed and the turbine speed to deliver the desired torque at the torqueconverter output.

Drive line disturbances in the systems of FIGS. 1-3 may also be reducedvia the driveline disconnect clutch. One example approach opens thetorque converter clutch prior to actuating the driveline disconnectclutch. For example, the driveline disconnect clutch may be opened whenthe engine is commanded to shutdown, either during a vehicleregenerative braking condition and/or when the vehicle comes to a stopand the engine is shutdown.

In another example, during regenerative braking, the drivelinedisconnect clutch may be open, the engine may be stopped, and the torqueconverter may be locked in order to increase the braking torque that canbe absorbed in the DISG 240. After the engine is shutdown, the drivelinedisconnect clutch remains open until the beginning of the engine restartprocess. During the engine restart, the driveline disconnect clutch maybe partially closed to crank the engine until the first combustion eventin a cylinder. Alternatively, the driveline disconnect clutch may bepartially closed until the engine reaches a predetermined speed aftercombustion in a cylinder is initiated. Once the engine combustion issufficiently restarted and the engine and driveline disconnect clutchspeed are sufficiently close (e.g., within a threshold RPM value), thedriveline disconnect clutch capacity is ramped up to close and holdwithout slip. During driveline disconnect clutch ramping, torquedisturbances at the driveline disconnect clutch output may be present.Consequently, torque feedback from the open torque converter or a torquesensor may be the basis for adjusting a DISG speed setting. Operatingthe DISG in speed control mode may allow desired torque values to bemaintained with more consistency until the driveline disconnect clutchis fully closed. After the driveline disconnect clutch is closed, thetorque converter clutch (TCC) may be locked based on a lock-up schedule(e.g., TCC may be actuated based on accelerator pedal position andvehicle speed).

In this way, the torque converter clutch may be fully opened prior tothe beginning of the engine restart process. The torque converter clutchmay be closed after the engine has restarted and the drivelinedisconnect clutch has fully closed. Additionally, while the drivelinedisconnect clutch is being closed, pressure to the driveline disconnectclutch is known (as it is being commanded by the controller) and therebyan estimate of the average driveline disconnect clutch torque isavailable. To further enhance the operation, this estimate of thedriveline disconnect clutch torque, or capacity, can be used by thecontroller as a feed-forward input to the DISG feedback speed control toimprove the disturbance rejection response. The driveline disconnectclutch capacity which is based on a torque estimate may then be added asan input to an inner torque feedback loop in the electric machine(DISG). The inner loop is an inner current loop which may be the basisfor improving the response of the DISG when the DISG is in speedfeedback mode.

In this way, one example approach for operating a vehicle having apowertrain, such as the powertrain described with regard to FIGS. 2-3,includes first operating with the vehicle stopped or with a speed belowa threshold, and with the engine at rest and the driveline disconnectclutch open. Next, with the torque converter fully unlocked, the methodincludes receiving a request to launch the vehicle, such as based on anoperator pedal input increasing past a threshold amount. In response,the engine is cranked and started with one or more of the DISG 240 and astarter motor while the driveline disconnect clutch is closed, againwith the torque converter still unlocked. During this operation, torquefeedback from the torque converter input/output speeds is used toestimate the torque at shaft 241, which is compared with a desiredtorque value and it provides adjustment to a speed setting of the DISG240, which is in speed control mode. For example, the speed setting maybe an adjustment parameter that drives torque error between estimatedand desired torque at shaft 241 toward zero.

In addition to the above operation, additional control actions can alsobe taken, particularly with regard to lash crossing. For example, whenthe driver tips-in while the vehicle is in a regeneration mode with theengine off (e.g., at rest), the driveline transitions from negativetorque to positive torque, the engine is started, and the drivelinedisconnect clutch closes, with all of these actions being coordinated soas to introduce minimal torque disturbances at the wheels. Underselected conditions, these actions are carried out while maintaining thetransmission 208 at a fixed gear (e.g., without changing transmissiongear). However, the starting of the engine and the crossing of the lashcan generate such disturbances. As such, during the transition thedriveline torque may be controlled from small negative to a smallpositive torque during lash crossing and then to the demanded torque.Such limitation of engine torque, however, can introduce delay indelivering the driver demanded torque, which when added to the delay ofrestarting the engine, can cause considerable driver dissatisfaction.

In one approach, coordination of the torque converter bypass clutch 212capacity and the DISG 240 output may be used. For example, timing ofconverting the DISG from torque control to speed control may be alignedwith engine restarting conditions and transition through the lash regionto reduce disturbances to the driveline caused by the engine startingand crossing through the lash region.

In one example, operation is provided for conditions where the driver isapplying the brake and the vehicle is in a regeneration mode, the engineis off, the driveline disconnect clutch fully open, and the DISG isabsorbing torque. The DISG is generating a desired level of brakingtorque (and storing generated electricity in the battery, for example).During these conditions, the driveline is undergoing negative torque andthe torque converter bypass clutch 212 is locked. The amount of negativetorque at the DISG may be increased and applied through the driveline soas to increase regeneration. The amount of negative torque may be basedon a desired wheel braking torque for the present operating conditions.The negative braking may be based on a degree to which the driver isactuating a brake. However, negative braking may also occur while theoperator has both the brake pedal and accelerator pedal released.

When the driver releases the brake (if it was applied) and tips-in tothe accelerator pedal, the vehicle transitions to engine on operationwith positive driveline torque delivering a demanded torque level. Asnoted above, during this transition, with no transmission gear changes,the torque crosses through zero torque (lash zone) and the engine iscranked and started. The inventors herein have recognized that theengine cranking torque disturbance is upstream of the clutch 212, butthe lash disturbance is downstream of the clutch 212. The capacity ofclutch 212 may be coordinated with the speed of the DISG to reduce thesedriveline disturbances.

For example, the TCC 212 capacity may be reduced enough to allowcontrolled slip as the regeneration torque is decreased. Such operationmay help to isolate the driveline from the engine cranking torquedisturbance. As the DISG regeneration torque transitions from thecurrent value down towards zero torque, the driveline may transitionfrom a large negative torque down to near zero torque. Near zero torque,the driveline may enter the lash region. The control of the DISG is thenswitched from torque control mode to speed control mode and the torqueconverter impeller speed (Ni) is adjusted to a fixed speed above thetorque converter turbine speed (Nt).

Adjusting torque converter impeller speed this way provides a smallpositive torque during the crossing of the lash region and reduces thedisturbance to the driveline associated with crossing the lash region.The DISG desired speed may be increased to provide torque to the wheelsand provide some vehicle acceleration. An estimate of the amount oftorque required to crank the engine may be determined by the controllerto provide a feed-forward DISG torque command. The feed-forward DISGtorque command may reduce speed disturbances at the torque converterimpeller as the driveline disconnect clutch is engaged and the engine iscranked. The capacity of the driveline disconnect clutch is adjusted toreduce driveline disturbances. Once the engine has started and thedriveline disconnect clutch is closed, the engine may be transitionedinto torque control and deliver the desired torque.

As described above herein with regard to the system of FIGS. 1-3, forexample, torque disturbances may occur when the driveline disconnectclutch is actuated. Torque disturbances may lead to degraded drivabilityand NVH. For example, torque disturbances (e.g., due to a clutchactuation error, or clutch stick-slip, or an error between the commandedand actual engine torque) at the driveline disconnect clutch output maybe transferred to the transmission input and to the wheels as a functionof the transmission clutch state (e.g., degree of engagement of thedriveline disconnect clutch, such as based on pressure or slip ratio)and the transmission gear ratio.

The torque produced by the DISG 240 may in some examples be a functionof three phase current. The torque at the DISG output shaft 241 is a sumof DISG output torque and the torque at the DISG or electric machineinput. The DISG may be commanded by a powertrain control module (e.g.,controller 12) to operate in either a speed feedback mode or a torquemode. The controller provides the commanded speed or torque. Thecontroller or an inverter uses feedback of either the DISG speed sensoror the DISG current to produce the desired speed or torque.

For example, DISG torque may be output from a function or table thatincludes empirically determined values of DISG torque based on DISGspeed and current. In some designs the DISG output is connected to alaunch clutch which is modulated during shift events to shape or smooththe torque output of the DISG before it is transferred to the wheels. Inother applications, the DISG output is connected to a torque converter206 with a lock-up clutch. In designs that use a launch clutch insteadof a torque converter, the ability of the launch clutch to accuratelyand rapidly control the clutch torque at low torque levels may bechallenging. For example, the launch clutch may slip in the presence ofthe maximum torque output of the engine plus DISG. Therefore, the launchclutch may be designed with a high torque capacity. However, it may bedifficult to accurately control the launch clutch at low torque levelsthat may be used during an engine restart and during vehicle launch fromzero and/or low vehicle speeds.

One approach to adjust or control a launch clutch is to use a torquesensor that is mounted on the launch clutch input shaft. The torquesensor installation deposits a shaped magnetic layer on the launchclutch input shaft which generates a voltage output that is proportionalto shaft torque. The voltage is read by a non-contacting sensor(s) andsensing system. The torque signal from the torque sensor can then beused to operate the DISG in a closed loop torque feedback mode to canceltorque disturbances that appear at the driveline disconnect clutchoutput (DISG input). If the automatic transmission uses a torqueconverter clutch at the transmission input, a torque sensor may bemounted on the torque converter input shaft. The torque converter inputshaft torque sensor may be used to provide feedback in the DISGcontroller to reject torque disturbances transmitted by the drivelinedisconnect clutch.

As described herein, the engine may be shutdown, to zero speed (and thedriveline disconnect clutch opened), to reduce fuel consumption when theoperator releases the accelerator pedal. Therefore, the engine isshutdown when the vehicle is coming to a stop or another other time whenthe torque from the DISG is sufficient to accelerate the vehicle orovercome the road load. When the operator applies the accelerator pedaland the desired torque exceeds that which the DISG can provide, theengine is restarted to supplement the DISG output torque. In addition,the engine can be restarted during a coasting condition if the batterystate of charge drops below a minimum threshold. The engine may berestarted to provide positive driveline torque and to provide torque toallow the DISG to operate as a generator to recharge the battery. Duringthe engine restart process, either the driveline disconnect clutch or aseparate starter motor may be used to crank the engine depending onoperating conditions as described herein. Once combustion commences inthe engine, either the engine is accelerated to match the input speed ofthe DISG, or the driveline disconnect clutch engagement/slip iscontrolled by controlling the clutch pressure to pull the engine up tothe DISG input speed. As the driveline disconnect clutch closes, a largetorque disturbance may be generated at the driveline disconnect clutchoutput which may then be transmitted to the DISG output. A torquedisturbance can be potentially transmitted to the transmission outputand the wheels, thereby degrading vehicle drivability and NVH.

Various approaches may be used to reduce the impact of this enginerestart torque disturbance, such as those that have already beendescribed herein. Alternatively, or additionally, one method to reducethe amplitude of the engine restart torque disturbance at the drivelinedisconnect clutch output is to match the engine crankshaft speed to thedriveline disconnect clutch output, or DISG (as the two are connected bya shaft) speed, before the driveline disconnect clutch is closed. Suchan approach makes use of the driveline disconnect clutch output torqueto driveline disconnect clutch speed difference relationship. Inparticular, the driveline disconnect clutch output torque is effectivelymultiplied by the sign of the driveline disconnect clutch input andoutput speed difference. For example, it is approximately equal to thesign (crankshaft speed−DISG speed). The closer these speeds are matched,the lower the driveline disconnect clutch output torque.

While such an approach can be used to reduce the driveline disconnectclutch output toque disturbance, it operates to accelerate the enginespeed to driveline disconnect clutch output speed. The drivelinedisconnect clutch output speed may vary from 750 to 3,000 RPM.Accelerating the engine to a speed in this range may delayengine-powered launch and the response to a driver tip-in. For example,until the driveline disconnect clutch is closed, the engine eitherprovides no torque at the transmission input or acts as a drag (e.g., ifcrankshaft speed<DISG speed, then the driveline disconnect clutch outputtorque is negative). If the driver tips-in (e.g., depressed theaccelerator pedal) and the DISG does not have sufficient torque capacityat the present DISG speed, then the desired torque may not be provideduntil the driveline disconnect clutch is closed and the engine is ableto provide a positive torque.

Thus, under some conditions, is may be desirable to use to the drivelinedisconnect clutch to pull the engine speed up to the DISG speed to morerapidly close the driveline disconnect clutch and provide positiveengine torque at the DISG output. The difficulty with closing thedriveline disconnect clutch while the engine is accelerating to the DISGspeed is that the torque at the driveline disconnect clutch output is afunction of sign (crankshaft speed−DISG speed). If the DISG is beingused to accelerate the crankshaft and dual mass flywheel inertia, thenthe difference between the engine combustion torque and the DISG torquethat is applied to achieve a given acceleration level will appear at theDISG output as a negative torque that will then suddenly change sign toa positive torque when the crankshaft (or dual mass flywheel output)speed exceeds the DISG speed.

A change in the driveline disconnect clutch output torque may create atorque spike at the DISG input which may be transferred to thetransmission input and/or wheels. Therefore, the DISG can be operated asa torque disturbance rejection device to reduce the engine restarttorque increase. The torque at the DISG output is the sum of the DISGoutput torque and the driveline disconnect clutch output torque. Controlof the DISG may be based on detection of the torque disturbance at oneor more of the driveline disconnect clutch output, at the DISG output,at the torque converter output, and/or at the transmission output. Thetorque sensor may allow the DISG to reject the torque disturbancedirectly. Such torque sensing can be provided by a non-contactingtransmission shaft torque sensor.

If such a sensor is applied to the shaft between the drivelinedisconnect clutch and the DISG rotor, the sensed torque can be input tothe DISG control to create an opposite torque to cancel the enginerestart driveline disconnect clutch output torque spike. Alternatively,the torque sensor can be located on the shaft between the DISG rotor andthe torque converter (or impeller). In such an example, the inertia andacceleration of the DISG rotor are included and accounted for in thedisturbance rejection torque calculation. Further, a transmission inputor output shaft torque sensor may be applied. If a transmission outputshaft torque sensor is applied the disturbance rejection torque term mayinclude compensation for the transmission inertias and optionally theclutch states.

Referring now to FIG. 4, a flowchart of an example method to operate avehicle driveline with the methods of FIGS. 5-47 is shown. The method ofFIG. 4 and subsequent methods may be stored as executable instructionsin non-transitory memory of controller 12 shown in FIGS. 1-3. Further,vertical markers such as T₀-T₈ shown in FIG. 10 indicate times ofinterest during the following illustrated sequences.

At 402, method 400 determines operating conditions. Operating conditionsmay include but are not limited to torque demand, engine speed, enginetorque, DISG speed and torque, vehicle speed, ambient temperature andpressure, and battery state of charge. Torque demand may be derived fromaccelerator pedal 130 and controller 12 of FIG. 1. Method 400 proceedsto 404 after operating conditions are determined.

At 404, method 400 adjusts driveline operation and operating parametersaccording to the methods of FIGS. 5-8. In particular, method 400 adjustsdriveline operation in response to driving route conditions and/ordriver behavior. Method 400 proceeds to 406 after driveline operationand operating conditions are adjusted.

At 406, method 400 adjusts driveline or powertrain operation for vehiclemass as described in FIGS. 9 and 10. In one example, timing andconditions for engine stopping may be adjusted in response to vehiclemass so that driveline wear and the number of driveline disconnectclutch state changes may be reduced. Method 400 proceeds to 408 afterdriveline operation for vehicle mass is adjusted.

At 408, method 400 judges whether or not an engine start is desired. Anengine start may be requested via an operator key or pushbutton inputthat has a sole function of requesting an engine start and/or stop.Alternatively, an engine restart may be automatically requested bycontroller 12 based on operating conditions not including driveroperation of a device that has a sole function of requesting enginestopping or starting. For example, controller 12 may request an enginestart in response to a driver releasing a vehicle brake pedal or inresponse to a battery state of charge. Thus, a request to restart theengine may be initiated via inputs that have functions other than solelyrequesting an engine start. If method 400 judges that an engine restartis requested, method 400 proceeds to 410. Otherwise, method 400 proceedsto 418.

At 410, method 400 selects a device for starting an engine as describedin FIGS. 11 and 12. In one example, the engine may be started via astarter that has a lower power output than the DISG. In another example,the engine may be started via the DISG while the starter with lowerpower output remains deactivated. Method 400 proceeds to 412 after theengine starting means is selected.

At 412, method 400 adjusts fuel injection timing of one or more directfuel injectors supplying fuel to an engine as described in FIGS. 13 and14. The fuel injection timing is adjusted to provide a single ormultiple fuel injections during a cycle of a single cylinder. Byadjusting the fuel injection timing, the engine speed profile duringengine run-up (e.g., engine acceleration from cranking speed (e.g., 250RPM)) to the desired engine idle speed. Method 400 proceeds to 414 afterfuel injection timing is adjusted.

At 414, method 400 judges whether or not the engine start istransmission shift related. For example, method 400 judges if it isdesirable to start the engine based on shifting from one transmissiongear to another transmission gear. If method 400 judges that it isdesirable to start the engine based on transmission shifting orforecasted transmission shifting, method 400 proceeds to 416. Otherwise,method 400 proceeds to 418.

At 416, method 400 starts the engine during transmission shifting asdescribed in FIGS. 15-18. In one example, the engine may be startedbefore gear clutches are opened or closed during a shift. Method 400proceeds to 418 after starting the engine.

At 418, method 400 provides dual mass flywheel (DMF) compensation.Further, method 400 may provide driveline disconnect clutchcompensation. DMF compensation may dampen torque transfer across the DMFby controlling the DISG torque and/or speed as well as drivelinedisconnect clutch torque. DMF compensation is provided as described inFIGS. 19-22. Method 400 proceeds to 420 once DMF compensation isinitiated.

At 420, method 400 judges whether or not it is desirable to stop theengine from rotating. Method 400 may judge that it is desirable to stopthe engine from rotating during low torque demand conditions and/orother conditions. Method 400 proceeds to 422 if it is judged desirableto stop the engine from rotating. Method 400 proceeds to 420 if it isjudged not to stop the engine from rotating.

At 422, method 400 adjusts the engine stopping profile. In one example,engine speed during engine deceleration to zero rotational speed isadjusted so that the engine position at zero engine speed is desirablefor restarting the engine. The engine stopping profile may be adjustedas described in FIGS. 23-26. Method 400 proceeds to 424 after the enginestopping profile has been selected and/or adjusted.

At 424, method 400 adjusts powertrain operation for hill holdingconditions. In one example, the powertrain is selectively adjusted inresponse to vehicle road grade. Method 400 proceeds to exit after thepowertrain is adjusted in response to vehicle road grade.

At 430, method 400 judges whether or not vehicle braking via thedriveline is desired. Method 400 may judge that it is desirable toprovide vehicle braking via the driveline when the vehicle is descendinga hill or during other conditions. If method 400 judges that it isdesirable to brake the vehicle via the driveline, method 400 proceeds to432. Otherwise, method 400 proceeds to 434.

At 432, method 400 adjusts DISG and engine operation to provide adesired level of vehicle braking via the driveline as described in FIGS.29A-36. In one example, vehicle braking is provided via the DISG whenbattery state of charge (SOC) is less than a threshold level. Method 400proceeds to 434 after vehicle braking via the driveline is provided.

At 434, method 400 judges whether or not to enter or exit sailing mode.In one example, sailing mode may be described as when the engine isoperating at sailing idle speed (e.g., combusting air and fuel) whilethe driveline disconnect clutch is open. The sailing idle speed is lowerthan the engine idle speed when engine is combusting an air-fuel mixtureand the driveline disconnect clutch is closed. Additionally, the enginemay be operated in an Atkinson cycle mode while in sailing mode.Further, in some examples spark timing may be advanced to near or atminimum spark timing for best engine torque (MBT). In one example,sailing mode may be entered when DISG torque is within a predeterminedrange of a threshold DISG torque. Method 400 proceeds to 436 if it isjudged desirable to enter or exit sailing mode. Otherwise, method 400proceeds to 438.

At 436, method 400 may operate the engine and driveline in a sailingmode where the engine operates at an efficient operating condition andwhere the driveline disconnect clutch is open while the DISG isproviding torque to the vehicle driveline as described in FIG. 38.Alternatively, method 400 may exit the sailing mode as described in FIG.39. Method 400 proceeds to 438 after sailing mode has been entered orexited.

At 438, method 400 judges whether or not to adjust the transfer functionof the driveline disconnect clutch. In one example, method 400 judgeswhether or not to adapt the transfer function of the drivelinedisconnect clutch during selected conditions such as during engine idleor engine stop conditions. If method 400 judges that it is desirable toadjust the transfer function of the driveline disconnect clutch, method400 proceeds to 444. Otherwise, method 400 proceeds to 440.

At 444, method 400 adjusts or adapts the transfer function of thedriveline disconnect clutch as described in FIGS. 42-45. In one example,the driveline disconnect clutch transfer function describes the torquetransfer of the driveline disconnect clutch based on torque input to thedriveline disconnect clutch and the pressure supplied to the clutch(e.g., the hydraulic oil pressure supplied to the driveline disconnectclutch or the duty cycle of an electrical signal supplied to thedriveline disconnect clutch). Method 400 proceeds to exit after thedriveline disconnect clutch transfer function is adjusted or adapted.

At 440, method 400 operates the engine and DISG to provide a desiredtorque to the input of the transmission. In one example, the engine andDISG are operated depending on driveline torque demand provided by adriver and/or controller. For example, if 35 N-m of driveline torque atthe torque converter impeller is requested the DISG may provide 10 N-mto the driveline while the engine provides the remaining 25 N-m to thedriveline. Alternatively, the DISG or engine may provide all 35 N-m tothe driveline. Operating conditions of the engine and/or DISG may alsobe considered to determine the amounts of torque output by the engineand DISG. Method 400 proceeds to 442 after the engine and DISG operatingmodes, speeds, and torques are output.

At 442, method 400 adjusts engine and DISG torque to provide a desiredtorque at the torque converter impeller. In one example, torque at thetorque converter impeller is estimated via a torque sensor. In otherexamples, the torque converter operating state is a basis for estimatingtorque at the torque converter impeller. The torque converter impellertorque estimate is as described in FIG. 21. The estimated transmissionimpeller torque is subtracted from a desired transmission impellertorque to provide a torque converter impeller torque error. Enginetorque and/or DISG torque are adjusted in response to the torqueconverter impeller torque error to reduce the torque converter impellertorque error toward zero. Method 400 proceeds to exit after thedriveline torque is adjusted.

Referring now to FIG. 5, a schematic diagram of example information thatmay be encountered during driving from one location to another locationis shown. The sources of information shown in FIG. 5 are available tothe methods shown in FIGS. 6-8. Further, the sources of information anddevices shown in FIG. 6 are available to the systems shown in FIGS. 1-3.

In this example, vehicle 290 may travel route number one 501 or routenumber two 502 to first and second destinations respectively. Vehicle290 may include a solar charging system 504 for charging energy storagedevice 275 shown in FIG. 2. The solar charging system may include solarpanels and other related devices. Additionally, vehicle 290 may includean inductive charging system 514 for charging energy storage device 275shown in FIG. 2. Inductive charging system 514 may receive charge from apower source external to the vehicle while the vehicle is moving.Vehicle 290 also includes a receiver 503 for receiving signals thatoriginate from external or within the vehicle 290.

Vehicle route number one includes several sources of information,objects, and elements that may be the basis for selectively operatingcertain driveline components. For example, vehicle 290 may receiveglobal positioning system (GPS) information from satellite 505 during acourse of a trip. The GPS system may provide information that allowsprocessor 12, as shown in FIG. 1, to determine road grades and distancesalong route number one. Processor 12 may also store informationregarding vehicle stops that are based on signs or signals 506 during acourse of a trip so that when vehicle 290 travels route number one againthe information is available to determine when the vehicle will stop,start, accelerate, decelerate, or cruise at a substantially constantspeed (e.g., +5 MPH).

Vehicle 290 may also estimate an amount of charge provided by solarsystem 504 via sun 507 during driving route number one to energy storagedevice 275. For example, if the vehicle begins to travel route numberone making 1 watt/minute at 1:00 P.M. and it is expected that it willtake one hour to travel route number one, it may be estimated that 60watts will be produced during the course of traveling route number one.Further, the estimated power produced during the course of the trip maybe adjusted based on the time of day and forecasted weather. Forexample, an amount of electrical power produced at specific time of daycan be extrapolated to an amount of power that will be produced laterthat day based on empirically determined solar tables and the time ofday.

Vehicle 290 may also record and store to memory or receive roadconditions 508 from external sources such as GPS. Road conditions 508may include road grade information, road surface information, and speedlimits Vehicle 290 may also receive or measure ambient temperature fromtemperature sensor 509. Temperature sensor 509 may be incorporated intovehicle 290 or it may be external to vehicle 290.

Finally on route number one, vehicle 290 may receive electrical power atpower source 510. Power source 510 may be a residential or commercialpower source that supplies power to vehicle 290 from an electrical gridat destination one. Vehicle 290 may have stored information including astored database and/or information stored from previous trips todestination one that indicate vehicle 290 may be recharged atdestination one. Such information is useful for determining how electriccharge stored in vehicle 290 is used during the course of a trip.

In another example, vehicle 290 may travel to destination two via routenumber two. Vehicle 290 may be programmed to recognize that it istraveling to destination two. Along route number two, vehicle 290 mayreceive weather, road conditions, ambient temperature, and GPS data frominfrastructure 515. Infrastructure may include but is not limited toradio broadcast towers and highway/road broadcast devices. Vehicle 290may also receive road conditions from hand held devices 513 such asphones, computers, tablet devices, and/or personal organizers. In somesituations, vehicle 290 may receive road conditions and destinationinformation (e.g., availability of electrical charging stations) fromother vehicles 511 that supply information via a transmitter 512.

Thus, a vehicle may receive information at the beginning of a trip andthroughout the trip that may be a basis for controlling drivelineoperation. For example, the sources of information described in FIG. 5may be the basis for operating driveline disconnect clutch 236, DISG240, and engine 10 shown in FIG. 2.

Referring now to FIG. 6, a flowchart of a method for operating a hybridpowertrain in response to information encountered during driving fromone location to another location is shown. The method of FIG. 6 may bestored in non-transitory memory as executable instructions in the systemof FIGS. 1-3.

At 602, method 600 determines vehicle operating conditions. Vehicleoperating conditions may include but are not limited to engine speed,vehicle speed, ambient temperature, driver demand torque (e.g., torquedemanded by a driver via an input and may also be referred to as desireddriveline torque in some examples), and energy storage device SOC.Further, operating conditions may include selecting a route to adestination based on driver input or by matching a present driving routeto driving routes taken during previous trips. Method 600 proceeds to604 after vehicle operating conditions are determined.

At 604, method 600 captures driving route information. Method 600 mayreceive driving route information such as road grade, traffic signallocations, speeds of other vehicle, traffic backup locations, electricalcharging station locations, ambient temperature, and related trafficinformation from a variety of sources. The information sources mayinclude but are not limited to internal memory of a controller in thevehicle, hand held personal devices (e.g., personal organizers, tablets,computers, phones), satellites, infrastructure, other vehicles, andtraffic communication devices. In one example, a vehicle's driving routemay be compared to driving routes stored in controller memory. If thevehicle's present driving route matches a driving route stored incontroller memory, the controller selects the destination and drivingconditions (e.g., traffic signals, road grade, charging facilities,etc.) from the driving route stored in memory without driver input.Method 600 proceeds to 606 after driving route information is captured.

At 606, method 600 prioritizes use of stored electrical energy based onopportunities to charge the electrical energy storage device along aselected driving route. FIG. 7 shows one way to prioritize use of storedelectrical energy. Prioritizing use of stored electrical energy mayinclude only using electrical energy during selected vehicleaccelerations so that hydrocarbon fuel usage may be reduced as comparedto simply basing electrical energy use based on desired torque demand.Further, prioritizing use of stored electrical energy may include usingsubstantially all available stored charge (e.g., reduce energy storagedevice charge down to a threshold amount of charge) in the electricalenergy storage device when the vehicle is within a predetermineddistance of a way of externally charging the energy storage device orduring conditions where the energy storage device may be charged viakinetic energy (e.g., a hill descent). Method 600 proceeds to 608 afteruse of stored electrical energy is prioritized. In this way, method 600schedules use of stored electrical energy before the vehicle arrives atdriving route conditions that facilitate using the stored electricalenergy.

At 608, method 600 prioritizes charging of the electrical energy storagedevice via an engine based on a driving route. For example, method 600may operate an engine to propel a vehicle when an energy storage deviceSOC is low. Further, method 600 may operate the engine without chargingthe energy storage device when method 600 determines that the energystorage device may be charged a short time later using the vehicle'skinetic energy during vehicle deceleration. FIG. 8 shows one way toprioritize charging the electrical energy storage device. Method 600proceeds to 610 after electrical energy storage device charging has beenprioritized. In this way, method 600 schedules electrical energy storagedevice charging before the vehicle arrives at driving route conditionsthat facilitate electrical energy storage device charging.

At 610, method 600 prioritizes driveline sailing mode entry based on thevehicle's driving route. In one example, method 600 retrievesinformation from 702 of method 700 to determine when the vehicle isexpected to stop for less than a threshold amount of time. Further,method 600 may receive information pertaining to when the vehicle isexpected to accelerate above a threshold rate after the vehicle stopsfor less than the threshold amount of time. Method 600 schedules entryinto sailing mode (e.g., engine at idle, driveline disconnect clutchopen, and DISG providing requested torque to the vehicle driveline)based on locations in the drive route where the vehicle is expected tostop for less than a threshold amount of time and where the vehicle isexpected to accelerate from the vehicle stop at a rate that is greaterthan a threshold rate. Method 600 proceeds to 612 after sailing modeentry is scheduled. In this way, method 600 schedules sailing mode entrybefore the vehicle arrives at driving route conditions that facilitatesailing mode.

At 612, method 600 operates the driveline disconnect clutch, DISG, andengine based on scheduled and prioritized use of electrical energystored in the energy storage device, prioritized charging of theelectrical energy storage device via the engine, and sailing mode entry.In other words, method 600 may open and close the driveline disconnectclutch, operate the DISG, and operate the engine based on expectedvehicle and road conditions along a driving route. For example, ifmethod 600 schedules entry into sailing mode at a particular stop duringa driving route, method 600 opens the driveline disconnect clutch andenters sailing mode when the vehicle stops at the particular location.Further, method 600 opens the driveline disconnect clutch when the DISGis scheduled to provide torque to accelerate the vehicle withoutassistance from the engine in response to prioritizing use of electricalenergy stored in the electrical energy storage device. Further still,method 600 opens the driveline disconnect clutch in response to thevehicle being within a threshold distance before arriving at anelectrical charging station so that energy from the electric storagedevice may be used to propel the vehicle rather than the engine andhydrocarbons. Additionally, method 600 may open the driveline disconnectclutch in response being within a threshold distance before arriving ata downhill grade. Method 600 proceeds to 614 after driveline disconnectclutch operation is scheduled and carried out based on vehicle anddriving route conditions.

At 614, method 600 judges whether or not there has been a substantialchange in driving route and/or vehicle conditions. A substantial changein driving route or vehicle conditions may be a presence of anunexpected condition (e.g., an extended vehicle stop or unexpected lossof battery charge) or absence of an expected condition (e.g., no vehiclestop when a vehicle stop is expected). If method 600 judges that therehas been a change in driving route or vehicle conditions, the answer isyes and method 600 returns to 602 so that prioritization of storedelectrical energy, energy device charging, and sailing mode entry may bedetermined again. Otherwise, the answer is no and method 600 proceeds to616.

At 616, method 600 judges whether or not the vehicle is at its finaldestination for the trip. In one example, method 600 compares thevehicle's present location with a programmed destination. In anotherexample, method 600 compares the vehicle's present location with anexpected destination. If method 600 judges that the vehicle is at itsdestination, method 600 proceeds to exit. Otherwise, method 600 returnsto 614.

In this way, operation of a hybrid powertrain may be adjusted accordingto a driving route and conditions along the driving route. Adjustmentsto the hybrid powertrain may include but are not limited to opening andclosing a driveline disconnect clutch, charging an energy storage devicevia the engine, entering sailing mode, and entry and exit into or out ofother driveline operating modes.

Referring now to FIG. 7, a flowchart of a method for prioritizing use ofstored electrical energy in a hybrid vehicle is shown. The method basesuse of stored electrical energy on opportunities to charge an electricalenergy storage device over a driving route. The method of FIG. 7 may bestored in non-transitory memory as executable instructions in the systemof FIGS. 1-3.

At 702, method 700 determines a number of vehicle stops and theirlocations on a driving route and estimates regenerative energy suppliedto the electric energy storage device during vehicle stops and duringother opportunities (e.g., vehicle decelerations and during hilldecent). Method 700 may also estimate an expected amount of batterycharging via a solar charging system. Further, method 700 determines anumber of vehicle accelerations from stop and an estimate of electricalenergy to accelerate from each vehicle stop. Additionally, method 700may store information of vehicle stops that are less than a thresholdtime duration.

In one example, the number of vehicle stops and their locations areestimated based on a number of traffic signals and/or signs along thetravel route as determined from the information sources described inFIG. 5. In particular, in one example, the number of vehicle stops isdetermined from the number of traffic signals and/or signs along atravel route multiplied by a value representing a reasonable percentage(e.g., 60%) of the traffic signals at which the vehicle will actuallystop. The number of accelerations from stop equals the estimated numberof vehicle stops. The amount of energy regenerated during each vehiclestop may be calculated based on vehicle speed before the stop, roadgrade, and vehicle mass (e.g., using E=½ mv², where E is energy, m isvehicle mass, and v is vehicle velocity, or alternativelyF=m·a+m·g·sin(Θ) over the time interval where m is vehicle mass, a isvehicle acceleration, g is acceleration due to gravity, and e is theroad angle which can be converted to grade). Likewise, the amount ofenergy to accelerate the vehicle may be calculated based on the speedlimit, road grade, and vehicle mass (e.g., using F=m·a+m·g·sin(Θ) overthe time interval, or E=½ mv²) and then converted into electricalcharge. Further, energy obtained from solar or inductive devices alongthe route may be added to the total amount of charge available duringdriving the route. The number of traffic signals, their locations, andthe road grade information may be determined via the information sourcesshown in FIG. 5. Method 700 proceeds to 704 after the number of vehiclestops, vehicle accelerations, energy regenerated, and energy used toaccelerate the vehicle at each vehicle stop location is determined.

At 704, method 700 judges whether or not the energy storage device canprovide energy to accelerate the vehicle to the speed limit after everyvehicle stop determined at 702. In one example, the energy stored in theenergy storage device plus the amount of regenerative energy estimatedavailable along the driver route are added together. Driveline lossesare subtracted from the sum of stored energy and regenerative energy andthe result is compared to the amount of energy estimated to acceleratethe vehicle from all vehicle stops. If the amount of energy toaccelerate the vehicle from all vehicle stops is greater than the sum ofstored energy and regenerative energy, it may be determined that engineassistance may be necessary along the drive route and that the energystorage device may not have sufficient power stored to complete the tripover the route. If the energy storage device may not have sufficientpower to accelerate the vehicle from all stops along the selected route,the answer is no and method 700 proceeds to 706. Otherwise, the answeris yes and method 700 proceeds to 708.

At 706, method 700 selects which accelerations from stop will beperformed using energy from the energy storage device. In other words,method 700 decides during which vehicle accelerations the DISG willprovide torque to the driveline. In one example, the choice of vehicleaccelerations where the DISG is operated is based on which accelerationsfrom stop when combined require an amount of energy that most closelymatches the amount of energy available from the energy storage device.For example, if at the beginning of a trip an energy storage device isstoring X coulombs of charge, and the first twenty three vehicleaccelerations are expected to use X coulombs of energy, the first twentythree vehicle accelerations will be provided via the DISG and the energystorage device. However, it should be noted that the selected vehicleaccelerations do not have to be consecutive in order. Rather, individualvehicle accelerations powered via the DISG and energy storage device maybe selected from any acceleration during the scheduled vehicle route.

In another example, the accelerations from vehicle stop where the DISGis operated with charge from the energy storage device are based on whenenergy from regeneration is available to charge the energy storagedevice and an expected amount of energy stored at the time of vehiclestopping. For example, if only a small amount of regenerative energy isexpected during a vehicle deceleration and the energy storage devicecharge is expected to be less than a threshold level at a vehicle stop,the DISG is not scheduled to accelerate the vehicle from that particularvehicle stop. Method 700 proceeds to 716 after vehicle accelerationsfrom vehicle stop where the DISG is operated with charge from the energystorage device are determined.

At 708, method 700 determines a number of and locations of vehiclemoving accelerations not from vehicle stop. Method 700 also estimates anamount of energy to accelerate the vehicle during each moving vehicleacceleration. The locations and number of vehicle moving accelerationsmay be determined from where changes in speed limit over the course ofthe driving route occur. Thus, a number of moving vehicle accelerationsmay be determined from every increase in travel route posted speedlimit. The change in vehicle route speed may be stored in a map databaseand retrieved from memory. Further, the vehicle route may be determinedbased on the shortest distance or time between the vehicle's presentlocation and a requested destination.

Method 700 also determines the energy to accelerate the vehicle at eachof the vehicle acceleration locations. The amount of energy toaccelerate the vehicle may be calculated based on the speed limit, roadgrade, and vehicle mass (e.g., using F=m·a+m·g·sin(Θ) over the timeinterval, or E=½ mv²). Method 700 proceeds to 710 after the number ofmoving accelerations, locations of the moving vehicle accelerations, andenergy estimated to accelerate the vehicle at each moving vehicleacceleration location is determined.

At 710, method 700 judges whether or not the energy storage device canprovide energy to accelerate the vehicle to the speed limit after eachmoving vehicle acceleration is determined at 708. In one example, anyremainder in the amount of energy stored in the energy storage deviceplus the amount of regenerative energy estimated to be available alongthe driver route minus the energy to accelerate the vehicle at each stopdetermined from 702 is compared to an amount of energy to accelerate thevehicle at all moving vehicle acceleration locations. If the amount ofenergy to accelerate the moving vehicle at each location is greater thanthe remainder from 702, it may be determined that engine assistance maybe necessary along the drive route and that the energy storage devicemay not have sufficient power stored to provide electrical power overthe route. If the energy storage device does not have sufficient powerto accelerate the vehicle from all moving vehicle accelerations alongthe selected route, the answer is no and method 700 proceeds to 714.Otherwise, the answer is yes and method 700 proceeds to 712.

At 712, method 700 selects where during the driving route the remainingenergy stored in the energy storage device and produced duringregeneration (e.g., during vehicle deceleration) may be consumed. Forexample, if the energy storage device has X coulombs of charge remainingabove a threshold amount of charge and a charging source is available atthe vehicle destination, method 700 determines at what location alongthe drive route the remaining charge is consumed. In one example,consumption of the remaining charge stored in the energy storage deviceand not used to accelerate the vehicle is consumed beginning at alocation that is based on the destination. For example, if it isexpected that the vehicle will have Z coulombs of excess charge and thevehicle uses 1/Z coulombs per mile, the driveline disconnect clutch isopened and DISG begins discharging the Z coulombs Z miles away from thedestination and the engine is stopped. In this way, method 700 lowersenergy stored in the energy storage device in a way that may reducehydrocarbon fuel consumption since consumed stored electrical energy isincreased by consuming energy storage charge down to a threshold levelof charge (e.g., a minimum battery charge level). Further, since thevehicle may be recharged via the grid at the destination, the energystorage device may be charged with power from a more efficient sourcethan the engine.

On the other hand, if method 700 determines that there is no chargingsource at the destination, the driveline disconnect clutch is closed andthe energy may remained stored in the electrical energy storage device.Method 700 proceeds to 716 after it is determined where excess chargenot consumed during vehicle acceleration will be consumed.

At 714, method 700 selects which moving vehicle accelerations will beperformed with energy from the energy storage device. In other words,method 700 decides during which moving vehicle accelerations (e.g.,vehicle accelerations not from stop) the DISG will provide torque to thedriveline. In one example, the choice of moving vehicle accelerationswhere the DISG is operated is based on which moving vehicleaccelerations when combined require an amount of energy that mostclosely matches the amount of energy remaining after vehicleaccelerations from vehicle stop are provided energy to accelerate thevehicle. For example, if at the beginning of a trip an energy storagedevice is storing X coulombs of charge, and there are twenty threevehicle accelerations from stop that are expected to use Y coulombs ofenergy (e.g., where Y is smaller than X), the first twenty three vehicleaccelerations from vehicle stop will be provided via the DISG and theenergy storage device. If Z coulombs are expected to be left afteraccelerating the vehicle at each stop, and the energy consumption sum ofmoving vehicle acceleration energy is greater than Z coulombs, the firstmoving vehicle accelerations taking up to Z coulombs of charge areprovided the Z coulombs of charge. However, it should be noted that theselected moving vehicle accelerations where the excess charge isdelivered do not have to be consecutive in order. Method 700 proceeds to716 after moving vehicle accelerations receiving DISG assistance andcharge from the energy storage device are selected.

At 716, method 700 schedules DISG assistance to the driveline toaccelerate or to keep the vehicle moving based on the determinedlocations of accelerations and steady state energy use. The DISGassistance may be provided when the driveline disconnect clutch is in anopen state or during a closed state. Further, the DISG may provide allor only a portion of the torque to propel the vehicle.

In this way, it is possible to schedule and prioritize use of storedelectrical energy. In this example, vehicle accelerations from zerospeed have a higher priority than moving vehicle accelerations or ofusing stored electrical energy during cruise conditions. Such operationmay allow the engine to operate at more efficient operating conditionssuch as steady speed and load conditions.

Referring now to FIG. 8, a flowchart of a method for scheduling andprioritizing charging of an electrical energy storage device via anengine based on a driving route is shown. The method of FIG. 8 may bestored in non-transitory memory as executable instructions in the systemof FIGS. 1-3.

At 802, method 800 retrieves information from 702 and 708 of FIG. 7 todetermine when the electrical energy storage device is expected to needcharging. In particular, if it is determined at 702 of FIG. 7 that thevehicle may not accelerate from all zero speed conditions, method 800may determine that the electrical energy storage device needs to berecharged at a location of vehicle acceleration along the drive routewhere SOC is reduced to less than a threshold level. Likewise, method800 may estimate where along the drive route SOC is reduced to less thana threshold level during a moving acceleration or during cruiseconditions. Method 800 proceeds to 804 after determining when theelectric energy storage device is expected to need recharging.

At 804, method 800 judges whether or not the electrical energy storagedevice has sufficient charge to propel the vehicle over the entire trip.In one example, the SOC is compared against an estimate of energy tooperate the vehicle over the entire trip based on F=m·a+m·g·sin(Θ) overthe time interval, or E=½ mv². If method 800 judges that the electricenergy storage device has sufficient stored charge to operate the DISGover the entire driving route, the answer is yes and method 800 proceedsto exit. Otherwise, the answer is no and method 800 proceeds to 806.

At 806, method 800 determines portions and locations of the drivingroute where charging the energy storage device via the engine will bemost efficient and where the SOC is expected to be low. The SOC may beexpected to be low at locations determined at 702, 708, and 714 of FIG.7. The locations and portions of the driving route where charging theenergy storage device may be most efficient may be based on empiricallydetermined engine speeds and loads where the engine consumes least fuelfor each mile driven. For example, if it is determined that the engineoperates consuming least fuel for each mile driven at 2200 RPM betweenan engine load of 0.2 and 0.3, it may be determined that the energystorage device should be recharged via the engine at a vehicle speedwhere the engine is at 2200 RPM and between 0.2 and 0.3 load when theDISG is charging the energy storage device. Thus, in one example, method800 selects locations and portions of the driving route to charge theenergy storage device based on locations of roads having constantvehicle speeds (e.g., a 55 MPH speed limit) for extended durations(e.g., 10 miles) that correspond to efficient engine operatingconditions. In some examples, vehicle speeds are selected where engineefficiency is expected to be greater than a threshold efficiency. Theengine efficiency at a particular vehicle speed may be empiricallydetermined and stored in memory. Method 800 proceeds to 808 afterportions of the drive route where charging the energy storage device viathe engine is most efficient are determined.

At 808, method 800 determines locations and portions of the drivingroute where charge supplied by the engine to the energy storage devicemay be completely utilized. For example, method 800 estimates the amountof energy that may be used to propel the vehicle from its presentlocation, where charging the energy storage device via the engine isbeing considered, to the final destination. The energy storage devicemay be recharged at any location along the driving route where engineefficiency is greater than a threshold efficiency and where the amountof energy to propel the vehicle from its present location to itsdestination is greater than a threshold amount of charge (e.g., thecharge capacity of the energy storage device). Method 800 proceeds to810 after portions of the driving route where charge supplied by theengine to the energy storage device may be completely utilized.

At 810, method 800 selects locations and portions of the driving routewhere the engine may supply charge to the energy storage device mostefficiently and where charge supplied by the engine to the energystorage device can be completely utilized during the driving route. Forexample, if it is determined that the energy storage device storesenough energy to propel the vehicle for 10 miles and the vehicle is 20miles from the destination and operating at an efficiency that isgreater than a threshold efficiency, the location 20 miles from thedestination may be selected as a location for charging the energystorage device via the engine. The driveline disconnect clutch is closedwhen the engine is charging the electrical energy storage device via theengine. Method 800 proceeds to exit after locations where for chargingthe electrical energy storage device via the engine are selected.

In this way, energy storage device charging via the engine may beprioritized based on where the engine may operate efficiently duringcharging and based on the vehicle location being a distance away fromthe destination that allows for utilizing any charge that may besupplied to the energy storage device via the engine. Further, theprioritization may be the basis for determining locations of drivelinemode changes.

Thus, the methods and systems of FIGS. 1-8 provide for operating ahybrid vehicle, comprising: operating a driveline disconnect clutch inresponse to a vehicle destination. In this way, driveline operation maybe enhanced. The method includes where operating the drivelinedisconnect clutch includes opening the driveline disconnect clutch inresponse to information that a charging device is available at thevehicle destination. The method further comprises stopping an engine andreducing an amount of charge stored in an energy storage device inresponse to an estimate of energy the hybrid vehicle driveline will useto reach the vehicle destination. The method includes where the amountof charge is reduced via operating a driveline integratedstarter/generator. The method includes where operating the drivelinedisconnect clutch includes closing the driveline disconnect clutch inresponse to information indicating that a charging device is notavailable at the destination. The method further comprises closing thedriveline disconnect clutch and charging an energy storage device inresponse to a location of the vehicle destination.

The methods and systems of FIGS. 1-8 also provide for operating a hybridvehicle, comprising: receiving driving route information at acontroller; and selectively operating a driveline disconnect clutch inresponse to the driving route information. The method includes where thedriving route information includes whether or not a charging station isavailable at a destination, and where selectively operating thedriveline disconnect clutch includes opening the driveline disconnectclutch in response to an amount of energy the hybrid vehicle is expectedconsume to reach the destination.

In some examples, the method includes where the driving routeinformation includes an indication of a downhill grade, and where thedriveline disconnect clutch is held open in response to the indicationof the downhill grade. The method includes where the driving routeinformation is stored in the controller from a previous trip over thedriving route. The method further comprises accessing the driving routeinformation based on a present route of a vehicle and opening or closingthe driveline disconnect clutch in response to availability of chargingfacilities at a destination. The method also includes where selectivelyoperating the driveline disconnect clutch includes opening and closingthe driveline disconnect clutch in response to a number of expectedvehicle stops during a driving routes.

In one example, the method includes where selectively operating thedriveline disconnect clutch includes opening and closing the drivelinedisconnect clutch in response to a number of moving vehicleaccelerations not including vehicle accelerations from vehicle stop. Themethod includes where selectively operating the driveline disconnectclutch includes opening and closing the driveline disconnect clutch inresponse to a number of vehicle accelerations from vehicle stop.Further, the method includes where the driving route informationincludes road grade information, and further comprising storing chargein an electric energy storage device in response to the driving routeinformation.

The methods and systems of FIGS. 1-8 additionally provide for operatinga hybrid vehicle, comprising: assessing a state of charge (SOC) of anelectric energy storage device; receiving driving route information at acontroller; and scheduling charging the electrical energy storage deviceat a first location in response to the SOC and the driving routeinformation before reaching the first location. The method also includeswhere the hybrid vehicle receives driving route information from adifferent vehicle other than the hybrid vehicle. The method furthercomprises operating a driveline disconnect clutch in response to thedriving route information. The method further comprises updatingscheduling charging the electric energy storage device in response to achange in driving conditions. The method also further comprisesscheduling discharging the electrical energy storage device at a secondlocation before reaching the second location.

Referring now to FIG. 9, a flowchart of a method for an example sequencefor operating a hybrid vehicle powertrain in response to a varyingvehicle mass is shown. The method of FIG. 8 may be stored as executableinstructions in non-transitory memory in the system of FIGS. 1-3.Further, the method of FIG. 9 may provide the sequence illustrated inFIG. 10.

At 902, method 900 determines vehicle operating conditions. Vehicleoperating conditions may include but are not limited to engine speed,vehicle speed, energy storage device SOC, engine load, engine torquedemand, and vehicle acceleration. The operating conditions may bedetermined or inferred from the sensors described in FIGS. 1-3. Method900 proceeds to 904 after vehicle operating conditions are determined.

At 904, method 900 determines vehicle mass. In one example, vehicle massbased on the following equations:

Where vehicle acceleration is zero,

Engine/driveline torque≈road load+grade based torque

Using: T_wh1=R_rr·M_v·g·sin(θ₁)+T_r11

Where:

T_wh1=Wheel Torque on grade angle=θ₁

T_wh2=Wheel Torque on grade angle=θ₂

R_rr=Driven wheel rolling radius

M_v=vehicle mass estimate

g=gravity constant

θ₁=grade angle

T_r11=Road load torque at the driven wheel on grade 1

T_r12=Road load torque at the driven wheel on grade 2

Then the vehicle mass estimate is:

M _(—) v=[(T _(—) wh1−T _(—) wh2)+(T _(—) r12−T _(—) r11)]/[R _(—)rr*g*(θ₁−θ₂)]

In some examples, the vehicle mass includes mass of a vehicle and of atrailer being towed by the vehicle. In other examples, the vehicle massis the mass of only the vehicle without a trailer. Further, in someexamples, the vehicle mass may include mass of passengers in the vehicleand vehicle cargo. The engine\driveline torque may be estimated fromempirically determined torque maps or functions that are indexed usingengine speed and load. For example, engine torque may be estimated byindexing a map of engine torque output that is indexed by engine speedand load. Method 900 proceeds to 906 after vehicle mass is estimated.

At 906, method 900 adjusts the energy storage device SOC threshold whereautomatic engine stopping is allowed. In one example, the energy storagedevice SOC threshold is raised when the vehicle's mass is increased sothat the vehicle's engine will stop during vehicle decelerationconditions when the energy storage device is greater than a firstthreshold level. If the vehicle's mass is reduced, the energy storagedevice SOC threshold is reduced so that the vehicle's engine will stopduring vehicle deceleration conditions when the energy storage device isgreater than a second threshold level, the second threshold level lessthan the first threshold level. The energy storage device SOC thresholdmay be adjusted proportionately with a change in vehicle mass or as afunction of vehicle mass. FIG. 10 shows two SOC threshold levels thatare based on different vehicle masses. Method 900 proceeds to 908 afterthe energy storage device SOC threshold for engine stopping is adjusted.

At 908, method 900 judges whether or not conditions for automaticallystopping the engine are present. In some examples, conditions forautomatically stopping the engine include conditions indicating vehicledeceleration, brake pedal depression, absence of accelerator pedaldepression, and energy storage device SOC greater than a thresholdlevel. If method 900 judges that conditions for automatically stoppingthe engine are met, the answer is yes and method 900 proceeds to 910.Otherwise, the answer is no and method 900 proceeds to 912.

At 910, method 900 automatically stops the engine. The engine may beautomatically stopped via stopping fuel and/or spark to the enginewithout the driver requesting engine stop via a device that has a solefunction of stopping and/or starting the engine. Method 900 proceeds to912 after the engine is stopped.

At 912, method 900 judges whether or not the engine has beenautomatically stopped. In one example, a bit is set in controller memorywhen the engine is automatically stopped. If method 900 judges that theengine has been automatically stopped, the answer is yes and method 900proceeds to 914. Otherwise, the answer is no and method 900 exits.

At 914, method 900 judges whether or not vehicle mass is less than athreshold mass. In one example, the threshold mass is the vehicle massof an unloaded vehicle plus mass accommodations for one or more personsand a specified amount of cargo. If method 900 judges that vehicle massis less than a threshold mass, the answer is yes and method 900 proceedsto 916. Otherwise, the answer is no and method 900 proceeds to 922.

At 916, method 900 judges whether or not friction brake applicationforce is less than a threshold. Alternatively, method 900 judges whetheror not a brake pedal is applied at 916. If friction brake applicationforce is less than a threshold or if the brake pedal is not applied, theanswer is yes and method 900 proceeds to 918. Otherwise, the answer isno and method 900 proceeds to exit.

At 918, method 900 leaves the engine in a stopped state and provides athreshold amount of creep torque (e.g., torque that moves the vehicle ata predetermined slow rate of speed (2 mi/hr) on a flat grade) to vehiclewheels via the DISG. Method 900 proceeds to 920 after creep torque isoutput via the DISG.

At 920, method 900 provides a base amount of torque converter impellertorque in response to driver demand torque. The base amount of torqueconverter impeller torque does not account for any change in vehiclemass. Further, in one example, the base amount of torque converterimpeller torque is based on driver input to an accelerator pedal (e.g.,driver demand torque) and an amount of accelerator pedal deflection isconverted into a torque converter impeller torque. In other examples,wheel torque, engine brake torque, and/or other driveline relatedtorques may take the place of torque converter impeller torque. Thetorque converter impeller torque is converted into a desired DISGcurrent and the current is supplied to the DISG to provide the torqueconverter impeller torque.

At 922, method 900 judges whether or not friction brake applicationforce is less than a threshold. Alternatively, method 900 judges whetheror not a brake pedal is applied at 922. If friction brake applicationforce is less than a threshold or if the brake pedal is not applied, theanswer is yes and method 900 proceeds to 924. Otherwise, the answer isno and method 900 proceeds to exit.

At 924, the engine is restarted, the driveline disconnect clutch isclosed, and at least a portion of vehicle creep torque is provided bythe engine. In some examples, the vehicle creep torque may be providedvia the engine and the DISG. In other examples, the vehicle creep torqueis provided solely via the engine. Method 900 proceeds to 926 after theengine is started and at least a portion of vehicle creep torque isprovided by the engine.

At 926, method 900 provides a vehicle mass adjusted amount of torqueconverter impeller torque in response to driver demand torque. Forexample, method 900 provides a base amount of torque converter impellertorque plus an additional amount of torque that is based on the increasein vehicle mass. In one example, the additional amount of torque isempirically determined and stored in a table or function in controllermemory that is indexed by the vehicle mass that exceeds the base vehiclemass. The torque converter impeller torque may be provided solely viathe engine or via the engine and the DISG. In one example, the desiredtorque converter impeller torque is provided by opening the enginethrottle and supplying fuel to the engine in response to the desiredtorque converter impeller torque. In other examples, the desired torqueconverter impeller torque is provided via supplying the DISG with anamount of current and the engine with fuel and a throttle openingamount. Method 900 proceeds to exit after the desired torque converterimpeller torque is provided.

In this way, engine and driveline disconnect operation may be adjustedin response to a change in vehicle mass. Further, conditions forstopping the engine based on SOC may also be adjusted based on vehiclemass.

Referring now to FIG. 10, an example sequence for operating a hybridvehicle powertrain in response to varying vehicle mass is shown. Thesequence of FIG. 10 may be performed via the method shown in FIG. 10executed in the system described in FIGS. 1-3.

The first plot from the top of FIG. 10 is a plot of vehicle speed versustime. The Y axis represents vehicle speed and vehicle speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases in the direction of the X axis arrow.

The second plot from the top of FIG. 10 is a plot of engine operatingstate versus time. The Y axis represents engine operating state. Theengine is on and operating combusting an air-fuel mixture when the traceis at a higher level. The engine is off and not combusting when thetrace is at a lower level. The X axis represents time and time increasesin the direction of the X axis arrow.

The third plot from the top of FIG. 10 is a plot of vehicle brakeapplication state versus time. The Y axis represents vehicle brakestate. The vehicle brake pedal is applied when the trace is at a higherlevel. The vehicle brake pedal is not applied when the trace is at alower level. The X axis represents time and time increases in thedirection of the X axis arrow.

The fourth plot from the top of FIG. 10 is a plot of desired torqueconverter impeller torque versus time.

The Y axis represents desired torque converter impeller torque anddesired torque converter impeller torque increases in the direction ofthe Y axis arrow. The X axis represents time and time increases in thedirection of the X axis arrow.

The fifth plot from the top of FIG. 10 is a plot of energy storagedevice state of charge (SOC) versus time. The Y axis represents energystorage device SOC and energy storage device SOC increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases in the direction of the X axis arrow. Horizontal marker 1002represents a minimum energy storage device SOC level where the enginemay be stopped and the driveline disconnect clutch opened when vehiclemass increases via increasing vehicle payload, for example. Horizontalmarker 1004 represents a minimum energy storage device SOC level wherethe engine may be stopped and the driveline disconnect clutch openedwhen vehicle mass is that of the base unloaded vehicle. Thus, the enginemay be stopped and the driveline disconnect clutch opened at lower SOClevels when the vehicle it at its base mass. On the other hand, when thevehicle mass increases, the engine may be stopped and the drivelinedisconnect clutch opened at a higher SOC level so that the enginecontinues to operate unless the energy storage device is at a higherlevel SOC.

The sixth plot from the top of FIG. 10 is a plot of vehicle mass versustime. The Y axis represents vehicle mass and vehicle mass increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases in the direction of the X axis arrow.

The seventh plot from the top of FIG. 10 is a plot of drivelinedisconnect clutch state versus time. The driveline disconnect clutch isin an open state when the trace is at a lower level. The drivelinedisconnect clutch is in a closed state when the trace is at a higherlevel. The X axis represents time and time increases in the direction ofthe X axis arrow.

At time T₀, the vehicle speed is zero, the engine is stopped, the brakepedal is applied, the energy storage device SOC is relatively high, thedriveline disconnect clutch is open, and the vehicle mass is at a lowerlevel. In this example, the engine has been automatically stopped inresponse to vehicle speed being zero and the brake pedal being applied.

At time T₁, the driver releases the brake pedal and the vehicle speedgradually increases as the DISG (not shown) applies torque to thevehicle driveline in response to the driver releasing the brake pedal.The engine remains in an off state and the driveline disconnect clutchremains open. The desired torque converter impeller torque increases inresponse to the driver releasing the brake pedal and subsequentlyincreasing a driver demand torque. The driver demand torque may be anengine brake torque, torque converter impeller torque, wheel torque orother driveline torque. The vehicle mass remains at a lower level andthe energy storage device SOC starts to be reduced as the DISG solelypropels the vehicle.

At time T₂, the desired torque converter impeller torque has increasedto a level where the engine is automatically started and the drivelinedisconnect clutch is closed in response to a driver torque demand (notshown). The engine may be automatically started without direct operatorinput to a device that has a sole purpose of starting and/or stoppingthe engine (e.g., an ignition switch) when driver demand torque exceedsa threshold level of torque. The vehicle speed continues to increase inresponse to the increasing torque converter impeller torque. The vehiclemass remains at a lower level and the energy storage device SOCcontinues to be reduced as the vehicle accelerates. The vehicle brakepedal remains in an inactive position.

At time T₃, the vehicle begins to decelerate in response to a reduceddriver torque demand. The vehicle mass is at a lower level and theenergy storage device SOC is greater than the threshold level 1004 sothe driveline disconnect clutch is opened and the engine is stopped inresponse to the vehicle entering a deceleration mode as the driverdemand torque is reduced. The desired torque converter impeller torqueis reduced in response to the reduced driver demand torque. The vehiclebrake pedal state remains off and the energy storage device begins tocharge via the DISG converting vehicle inertia into electrical energy.

Between time T₃ and time T₄, the vehicle stops and the vehicle brake isapplied by the driver. The energy storage device SOC has increased andthe driveline disconnect clutch remains in an open state. The enginealso remains in an off state.

At time T₄, the vehicle mass is increased. The vehicle mass may increasewhen the driver or someone adds cargo or passengers to the vehicle, forexample. The vehicle speed remains at zero and the engine remains off.The desired torque converter impeller torque remains at a lower leveland the energy storage device SOC remains unchanged. The drivelinedisconnect clutch also remains in an open state.

At time T₅, the driver releases the brake pedal and the DISG torqueoutput increases as the desired torque converter impeller torqueincreases. The desired torque converter impeller torque increases inresponse to the driver releasing the brake and increasing the driverdemand torque. The energy storage device SOC begins to decrease as theDISG applies torque to the vehicle driveline. The vehicle speed beginsto gradually increase. However, since the vehicle mass has increased thevehicle accelerates at a lower rate. The controller begins to estimatethe change in vehicle mass based on the torque that is applied to thedriveline and the rate of vehicle acceleration.

Between time T₅ and time T₆, the engine is automatically restarted inresponse to the torque converter impeller torque increasing to greaterthan a threshold level. The driveline disconnect clutch is also closedin response to the torque converter impeller torque being greater than athreshold level. The energy storage device SOC decreases and the DISGprovides torque to the driveline.

At time T₆, the driver reduces the driver demand torque and applies thevehicle brake. The engine remains operating and the driveline disconnectclutch remains engaged so that the engine may provide braking during thevehicle deceleration. The engine remains operating because the vehiclemass has increased and because the energy storage device SOC is lessthan the threshold level 1002. Thus, the driveline disconnect clutchopening timing may be delayed or retarded as vehicle mass increases.Similarly, driveline disconnect clutch opening timing may be advanced asvehicle mass decreases. The vehicle mass remains at the higher level andthe vehicle decelerates toward zero speed. The energy storage device SOCincreases as the vehicle decelerates.

At time T₇, the driveline disconnect clutch is opened and the engine isstopped as vehicle speed approaches zero. The vehicle brake remains inan applied state and the desired torque converter impeller torqueremains at a lower level. The vehicle mass remains unchanged as thevehicle is stopped.

At time T₈, the brake pedal is released by the driver and the engine isautomatically started. In the present example, the driveline disconnectclutch is opened when the engine is stopped; however, in some examplesthe driveline disconnect clutch remains closed so that the engine andDISG accelerate to operating speed at the same time. The engine isrestarted upon release of the brake pedal in response to the increasedvehicle mass. In this way, it may be possible to reduce the possibilityof accelerating the vehicle at less than a desired rate since the engineand DISG are available as the brake pedal is released. Further, theengine and the DISG may apply a creep torque that propels the vehicle atthe same rate as when the vehicle is unloaded and when only propelledvia the DISG when the driver does not depress the vehicle acceleratorpedal.

The desired torque converter impeller torque is also increased inresponse to the increase in estimated vehicle mass. The desired torqueconverter impeller torque is increased so that the vehicle acceleratesin a similar way as when the vehicle is accelerated at a time when thevehicle mass is less (e.g., at time T₁). Thus, for a similar acceleratorpedal input, the vehicle accelerates similar to when the vehicle mass isreduced and the accelerator pedal input is the same. In this way, thedriver may experience similar vehicle acceleration for an equivalentaccelerator pedal input even when vehicle mass changes.

Thus, the methods and systems of FIGS. 1-3 and 9-10 provide foroperating a hybrid vehicle, comprising: adjusting operation of adriveline disconnect clutch in response to a change in vehicle mass. Themethod further comprises adjusting engine stopping timing in response tothe change in vehicle mass. The method includes where adjustingoperation of the driveline disconnect clutch includes delaying drivelinedisconnect clutch opening timing in response to an increase in vehiclemass. The method includes where adjusting operation of the drivelinedisconnect clutch includes advancing driveline disconnect clutch openingtiming in response to a decrease in vehicle mass. The method furthercomprises adjusting an energy storage device state of charge thresholdin response to vehicle mass. The method includes where adjusting theenergy storage device state of charge threshold includes increasing theenergy storage device state of charge threshold in response to vehiclemass.

In another example, the methods and systems of FIGS. 1-8 provide foroperating a hybrid vehicle, comprising: adjusting operation of adriveline disconnect clutch in response to a change in vehicle mass; andautomatically stopping an engine at a time that is responsive to thechange in vehicle mass. The method further comprises not restarting theengine in response to the vehicle mass when the vehicle mass is a firstvehicle mass. The method further comprises restarting the engine inresponse to the vehicle mass when the vehicle mass is a second vehiclemass. The method includes where the second vehicle mass is greater thanthe first vehicle mass. The method further comprises supplying at leasta portion of a creep torque via the engine after restarting the engine.

In some examples, the method includes where a creep torque is suppliedsolely via a DISG when the engine is not restarted and when the hybridvehicle is moved. The method further comprises adjusting a desiredtorque converter impeller torque in response to the change in vehiclemass. The method includes where adjusting the desired torque converterimpeller torque includes increasing the desired torque converterimpeller torque when the change in vehicle mass increases vehicle mass.The method includes where adjusting the torque converter impeller torqueincludes decreasing the torque converter impeller torque when the changein vehicle mass decreases vehicle mass.

In another example, the methods and systems of FIGS. 1-8 provide foroperating a hybrid vehicle, comprising: adjusting operation of adriveline disconnect clutch that is in communication with an engine inresponse to a change in vehicle mass; automatically stopping the enginein response to a first energy storage device state of charge beinggreater than a first threshold state of charge, the first thresholdstate of charge based on a first vehicle mass before the change invehicle mass; and automatically stopping the engine in response to asecond energy storage device state of charge being greater than a secondthreshold state of charge, the second threshold state of charge based ona second vehicle mass after the change in vehicle mass. Thus, thedriveline disconnect clutch may be operated to improve vehicleperformance based on vehicle mass.

In some examples, the method includes where the second threshold stateof charge is greater than the first threshold state of charge. Themethod includes where the second vehicle mass is greater than the firstvehicle mass. The method includes where the driveline disconnect clutchis open when the engine is stopped. The method also includes where thedriveline disconnect clutch is closed when the engine is stopped.

Referring now to FIG. 11, a flowchart of a method for starting an enginevia a first electric machine or a second electric machine is shown. Themethod of FIG. 11 may be stored in non-transitory memory of controller12 of FIGS. 1-3 as executable instructions.

At 1102, method 1100 determines vehicle operating conditions. Vehicleoperating conditions may include but are not limited to engine speed,DISG speed, vehicle speed, driveline torque demand, engine coolanttemperature, and driveline disconnect clutch operating state (e.g.,open, partially open, or closed). Method 1100 proceeds to 1104 afteroperating conditions are determined.

At 1104, method 1100 judges whether or not conditions are present tostop engine rotation. In one example, engine rotation may stop when thedesired driveline torque (e.g., combined torque provided via the engineand/or the DISG) is less than a threshold amount of torque. If method1100 judges that conditions are not present to stop engine rotation,method 1100 proceeds to 1106. Otherwise, method 1100 proceeds to 1110.

At 1106, method 1100 operates the engine. The engine is operated viaproviding spark and or fuel to the engine based on engine operatingconditions. In some examples where the engine is a diesel engine or ahomogeneous charge compression ignition (HCCI) engine, the engine may beoperated without spark. Method 1100 proceeds to 1108 after the engine isoperated.

At 1108, method 1100 provides torque from the engine to the vehiclewheels. Engine torque may be provided to the vehicle wheels by closingthe driveline disconnect clutch and directing engine output through thetransmission to vehicle wheels. In some examples, engine and DISG torquemay be supplied to vehicle wheels simultaneously. Method 1100 proceedsto exit after engine torque is provided to vehicle wheels.

At 1110, method 1100 stops engine rotation and opens or disengages thedriveline disconnect clutch. Engine rotation may be stopped byinhibiting fuel and/or air flow to engine cylinders. Method 1100proceeds to 1112 after the engine is stopped. Note that the DISG maycontinue to provide torque to vehicle wheels in response to driverdemand while the engine is stopped.

At 1112, method 1100 judges whether or not conditions are present torestart the engine. In one example, the engine may be restarted when thedriveline torque command exceeds a threshold torque amount. In otherexamples, the engine may be started when a temperature of a catalyst isreduced to less than a threshold temperature. If method 1100 judges thatselected conditions to restart the engine are present, method 1100proceeds to 1114. Otherwise, method 1100 returns to 1104.

At 1114, method 1100 determines an available amount of torque from theDISG. The amount of torque available from the DISG is based on the ratedDISG torque, battery state of charge, DISG speed, and DISG temperature.A table describing DISG available torque is stored in memory and isindexed via battery state of charge (e.g., battery voltage and amp hourrating), DISG speed, and DISG temperature. The table outputs the amountof available torque from the DISG. Method 1100 proceeds to 1116 afterthe amount of available DISG torque is determined.

At 1116, method 1100 judges whether or not the DISG has the capacity tostart the engine and provided the desired amount of torque. In oneexample, the desired amount of torque is determined at least in partfrom an accelerator pedal which the driver can adjust to vary thedesired driveline torque. The torque to start the engine may beempirically determined and stored in a table or function in memory. Thetable or function may be indexed via engine temperature and time sincelast engine stop. The table outputs a torque to reach a desired enginecranking speed (e.g., 250 RPM) from zero speed. The torque to start theengine is added to the desired driveline torque provided by the driver,and the amount of available DISG torque is subtracted from the sum ofthe torque to start the engine and the desired driveline torque. If theresult is positive, the DISG lacks the capacity to provide the torque tostart the engine and provide the desired driveline torque. Consequently,method 1100 proceeds to 1124. If the result is negative, the DISG hasthe capacity to provide the torque to start the engine and provide thedesired driveline torque. Therefore, method 1100 proceeds to 1118.

At 1118, method 1100 judges whether or not an engine start has beenrequested. If so, method 1100 proceeds to 1120. Otherwise, method 1100proceeds to 1122. Method 1100 may judge that an engine start request ismade when an engine torque request increases or when a driver releases abrake pedal, for example.

At 1120, method 1100 supplies DISG torque to vehicle wheels and to theengine. The DISG torque is provided to the engine via closing thedriveline disconnect clutch and transferring torque from the DISG to theengine. The driveline disconnect clutch may partially close to controlengine speed during engine starting. The engine may rotate at a crankingspeed (e.g., 250 RPM) or at a base idle speed (e.g., 800 RPM) beforefuel and spark are delivered to the engine. Method 1100 returns to 1104after DISG torque is provided to the engine and vehicle wheels.

At 1122, method 1100 supplies DISG torque to only vehicle wheels. TheDISG torque provided to the vehicle wheels may be based on acceleratorpedal input and/or input from a controller. Method 1100 returns to 1104after DISG torque is provided to vehicle wheels.

At 1124, method 1100 judges whether or not an engine start request ispresent. An engine start request may be occur as is described at 1118.If an engine start is requested, method 1100 proceeds to 1126.Otherwise, method 1100 proceeds to 1122.

At 1126, method 1100 starts the engine via a second electrical machinethat has a lower power output capacity than the DISG. For example, theengine may be started via a conventional starter that includes a pinionshaft and pinion gear that is selectively engaged to the engine flywheelto start the engine. The driveline disconnect clutch is closed when thesecond electrical machine is solely providing torque to rotate theengine. Further, fuel and spark are provided to the engine at 1126 toinitiate combustion in the engine so that the engine rotates under itsown power. Method 1100 proceeds to 1128 after the engine is started.

At 1128, method 1100 engages the driveline disconnect clutch to enabletransfer of torque from the engine to vehicle wheels. In one example,the engine speed is increased until the engine speed matches the speedof the DISG. The driveline disconnect clutch is closed when the enginespeed matches the DISG speed to reduce the possibility of introducing atorque disturbance to the driveline. Method 1100 proceeds to exit afterthe engine is started and delivering torque to vehicle wheels.

It should be noted that the method of FIG. 11 shows but one example ofstarting an engine solely via a lower power capacity electrical machine(starter motor) or solely via a higher capacity electrical machine(DISG). Other examples are also anticipated. For example, when both theDISG and lower power capacity starter motor are operational, the DISGand lower power capacity starter motor may start the engine duringdifferent operating conditions. However, if the DISG is deactivated, thelower power capacity starter may start the engine after the engine hasbeen automatically stopped from rotating during conditions where theDISG would otherwise start the engine. For example, the lower powercapacity starter may start the engine where the DISG is capable ofstarting the engine and providing torque to the driveline but for beingdeactivated. On the other hand, if the lower power capacity startermotor is deactivated, the engine may be started by the DISG when thedriveline torque demand is at a lower threshold level since the lowerpower capacity starter motor is unavailable.

Referring now to FIG. 12, a plot of an example sequence for starting anengine according to the method of FIG. 11 is shown. The vertical markersT₁₀-T₁₇ represent times of interest in the sequence. The sequence ofFIG. 12 may be provided by the system of FIGS. 1-3.

The first plot from the top of FIG. 12 represents DISG torque versustime. The X axis represents time and time increases from the left handside of the figure to the right hand side of the figure. The Y axisrepresents DISG torque and DISG torque increases in the direction of theY axis arrow. Horizontal line 1202 represents an amount of availableDISG torque. Horizontal line 1204 represents an amount of torque theDISG may provide to the transmission input while the DISG is crankingthe engine. The difference between horizontal lines 1202 and 1204represents an amount of torque to crank the engine for starting.

The second plot from the top of FIG. 12 represents engine speed versustime. The X axis represents time and time increases from the left handside of the figure to the right hand side of the figure. The Y axisrepresents engine speed and engine speed increases in the direction ofthe Y axis arrow.

The third plot from the top of FIG. 12 represents driveline disconnectclutch state (e.g., open or closed) versus time. The X axis representstime and time increases from the left hand side of the figure to theright hand side of the figure. The Y axis represents drivelinedisconnect clutch state and the driveline disconnect clutch state isopen at the top side and closed near the X axis as indicated.

The fourth plot from the top of FIG. 12 represents low power outputstarter state versus time. The X axis represents time and time increasesfrom the left hand side of the figure to the right hand side of thefigure. The Y axis represents low power output starter state and lowpower output starter state is engaged when the trace is at a higherlevel and disengaged when the trace is at a lower level.

The fifth plot from the top of FIG. 12 represents engine start requeststate versus time. The X axis represents time and time increases fromthe left hand side of the figure to the right hand side of the figure.The Y axis represents engine start request state and engine startrequest state is asserted to start or run when the trace is at a higherlevel. The engine start request is not asserted or indicating enginestop when the trace is at a lower level.

At time T₁₀, the DISG torque is at a lower level in response to a lowdriveline torque demand (not shown). The driveline torque demand mayoriginate from an accelerator pedal or other device and may beresponsive to a driver input. The engine is also stopped and thedriveline disconnect clutch is open. The lower power output starter isnot engaged and there is no engine start request.

At time T₁₁, an engine start request is provided while DISG torque isless than threshold 1204. The engine start request may be made inresponse to a battery state of charge (SOC) or other condition. The lowpower output starter remains inactive and the driveline disconnectclutch is closed shortly thereafter. Closing the driveline disconnectclutch transfers torque from the DISG to the engine, thereby crankingthe engine. The engine starts shortly after the DISG is at leastpartially closed. The driveline disconnect clutch may slip while theengine is being cranked and during engine run-up from engine stop toDISG speed.

At time T₁₂, the engine start/run request transitions to a low level inresponse to vehicle operating conditions (e.g., a charged battery and anapplied vehicle brake pedal). The driveline disconnect clutch is openedand the engine is stopped in response to the engine start/run request.The DISG continues to supply torque to the vehicle driveline.

Between time T₁₂ and time T₁₃, the DISG torque output increases inresponse to an increased driver demand torque (not shown). The engineremains off and the driveline disconnect clutch remains open.

At time T₁₃, the engine start/run request is asserted in response tobattery SOC being less than a threshold charge level (not shown). Thelow power output starter is activated as indicated since the DISG torqueis greater than the threshold torque at 1204. The driveline disconnectclutch is open while the engine is cranked by the lower power outputstarter. The low power output starter is deactivated when engine speedexceeds engine cranking speed.

At time T₁₄, the driveline disconnect clutch is closed after the enginespeed reaches the DISG speed. The engine start/run request remainsasserted and both the DISG and engine provide torque to the vehicledriveline.

At time T₁₅, the engine start/run request transitions to a lower levelto indicate the engine is to be stopped. Shortly thereafter, the engineis stopped and the driveline disconnect clutch is opened in response tothe engine start/run request transitioning to a lower level. The DISGcontinues to deliver torque to the vehicle driveline.

At time T₁₆, the engine start/run request is asserted in response to thedriver demand torque exceeding a threshold torque (not shown). Theengine is restarted so that the engine may output torque to thedriveline to augment DISG torque. The low power output starter isengaged in response to the engine start/run request transitioning to ahigher level. The low power output starter is disengaged in response toengine speed exceeding a threshold speed.

At time T₁₇, the driveline disconnect clutch is closed in response toengine speed reaching DISG speed. The engine and DISG supply torque tothe vehicle driveline after the driveline disconnect clutch is closed.

In this way, the engine may be started via the DISG or the lower poweroutput starter. The lower power output starter allows the DISG to outputa greater amount of torque to the driveline than would be possible ifonly the DISG had the capability of cranking the engine. Further, thelower power output starter allows the engine speed to reach DISG speedbefore the driveline disconnect clutch is closed so that little torquedisturbance may be noticed in the vehicle driveline.

Thus, the methods and systems of FIGS. 1-3 and 11-12 provide forstarting an engine, comprising: during a first condition, starting anengine with a first electrical machine while a driveline disconnectclutch is closed; and during a second condition, starting the enginewith a second electrical machine while the driveline disconnect clutchis open. The method includes where the second electrical machine has alower power output capacity than the first electrical machine. Themethod includes where the first electrical machine is a drivelineintegrated starter/generator (DISG), and where the driveline disconnectclutch has a first side mechanically coupled to a dual mass flywheel anda second side mechanically coupled to the DISG.

In some examples, the method includes where the first condition is adesired driveline torque that is less than a driveline torque during thesecond condition. The method includes where the driveline disconnectclutch is opened in response to a desired driveline torque. The methodincludes where the driveline disconnect clutch is closed when a sum of adesired driveline torque and an engine starting torque are greater thana threshold amount of torque. The method includes where the firstelectrical machine is positioned downstream of an engine and providestorque through a torque converter that rotates vehicle wheels, and wherethe second electrical machine is positioned at the engine and does notprovide torque through the torque converter to rotate vehicle wheelsabove an engine cranking speed that is lower than engine idle speed.

In other examples methods and systems of FIGS. 1-3 and 11-12 provide forstarting an engine, comprising: starting an engine via a firstelectrical machine when a desired torque demand is less than a firstthreshold amount; starting the engine via the second electrical machinewhen the desired torque demand is greater than the first thresholdamount; and supplying torque sufficient to rotate vehicle wheels solelyvia the first electrical machine during selected operating conditions.Thus, different electrical machines may start the engine duringdifferent conditions.

The method includes where the first electric machine is a drivelineintegrated starter/generator (DISG) and where the DISG is located in thehybrid vehicle driveline at a location between a driveline disconnectclutch and a transmission. The method includes where the DISG providestorque to start rotation of the stopped engine via at least partiallyclosing the driveline disconnect clutch. The method further comprisesdecoupling the second electrical machine from the engine when enginespeed reaches a threshold speed. The method includes where the secondelectrical machine includes a pinion shaft and a pinion gear. The methodincludes where the first threshold amount varies with battery state ofcharge. The method also includes where the first threshold amount varieswith speed of the first electrical machine.

The methods and systems of FIGS. 1-3 and 11-12 also provide for a hybridvehicle system, comprising: an engine; a starter selectively engaged tothe engine and including a pinion gear; a dual mass flywheel (DMF)including a first side mechanically coupled to the engine; a drivelinedisconnect clutch mechanically including a first side coupled to asecond side of the dual mass flywheel; a driveline integratedstarter/generator (DISG) including a first side coupled to a second sideof the driveline disconnect clutch; and a controller includingnon-transitory instructions executable to start the engine via thestarter during a first start and via the DISG during a second start.

In some examples, the hybrid vehicle system further comprises additionalinstructions to start the engine via the starter during conditions of adesired torque greater than a threshold. The hybrid vehicle systemincludes where the engine is started by rotating the engine via theDISG, and further comprising additional instructions to decouple theDISG from the engine after a predetermined number of combustion events.The hybrid vehicle system further comprises additional instructions tocouple the engine to the DISG after engine speed reaches DISG speed. Thehybrid vehicle system includes where available power output from thestarter is lower than available power output from the DISG. The hybridvehicle system further comprises additional instructions toautomatically stop the engine, and where the engine is started via theDISG based on an available amount of DISG output torque.

Referring now to FIG. 13, a flowchart of a method for adjusting fuelinjection to provide a desired engine speed trajectory during an enginestart is shown. The method of FIG. 13 may be stored as executableinstructions in non-transitory memory of controller 12 shown in FIGS.1-3.

At 1302, method 1300 judges whether or not engine starting is requestedand the driveline disconnect clutch is disengaged. Method 1300 may judgethat an engine start is desired when an engine starting variable isasserted in memory. Method 1300 may judge that the driveline disconnectclutch is disengaged when a driveline disconnect clutch state variableis not asserted in memory. If method 1300 judges that an engine start isdesired and a driveline disconnect clutch is not engaged, method 1300proceeds to 1304. Otherwise, method 1300 proceeds to 1316.

At 1304, method 1300 determines operating conditions. Operatingconditions may include but are not limited to DISG speed, enginetemperature, time since engine stop of rotation, and drivelinedisconnect clutch state. Method 1300 proceeds to 1306 after operatingconditions are determined.

At 1306, method 1300 determines desired engine speed based on torqueconverter impeller speed. Further, a desired cylinder air charge may bedetermined at 1306 so that the desired engine speed may be achieved. Inone example, the desired engine speed after engine run-up (e.g., fromcranking speed to a desired idle speed) is adjusted to the torqueconverter impeller speed. Thus, after engine run-up during an enginestart, the engine speed is controlled to the torque converter impellerspeed so that the driveline disconnect clutch may be closed to transferengine torque to vehicle wheels without creating a torque disturbance.The engine may be cranked via rotating the engine with a starter otherthan a DISG (e.g., a lower power output starter), if desired. Method1300 proceeds to 1308 after the desired engine speed is selected. Itshould be noted that torque converter impeller speed is equivalent toDISG speed since the DISG is coupled to the torque converter impeller.

At 1308, fuel injection for the first combustion event is adjusted. Inone example where the engine includes a near centrally located fuelinjector at the top of the combustion chamber, fuel is injected to atleast one cylinder via a single fuel pulse during a compression strokeof the cylinder and during a single cycle of the cylinder. The injectedfuel then participates in a first combustion event since engine stop forthe cylinder receiving the fuel. After the single fuel pulse is injectedto the cylinder, fuel injections during run-up may be injected in aseries of pulses during the intake and compression strokes of thecylinder receiving the fuel as described at 1310. In one example, asingle fuel pulse is injected to each of a predetermined number ofengine cylinders during the compression strokes of the cylinders. Thus,fuel is injected to each of the predetermined number of cylinders in oneor more pulses during a cycle of the cylinder receiving the fuel. Forexample, for a four cylinder engine, two engine cylinders receive asingle injection of fuel during the respective compression strokes ofthe cylinders receiving the single injection of fuel. The other twoengine cylinders received multiple injections of fuel during intakeand/or compression strokes of the cylinder receiving the fuel.

In a second example where the engine includes a fuel injection locatedat the side of the combustion chamber, multiple fuel injections for eachcylinder are delivered to a predetermined number of engine cylindersduring the compression stroke of the cylinder receiving the fuel for thefirst combustion event in the cylinder since engine stop. After apredetermined number of cylinders receive multiple fuel injectionsduring the compression stroke of the cylinder receiving the fuel,multiple injections of fuel may be supplied to each cylinder duringintake and/or compression strokes of the cylinder receiving the fuel.Additionally, the position of the engine throttle may be adjusted at1308 based on the desired engine speed. In one example, the enginethrottle opening amount is increased as the desired engine speedincreases during engine cranking. Method 1300 proceeds to 1310 afterfuel is injected for the first combustion events of each enginecylinder.

At 1310, method 1300 adjusts split fuel injection timing and fuelamounts based on desired engine speed and a speed differential betweenactual engine speed and desired engine speed. In particular, at lowerengine speeds (e.g., between cranking speed 250 RPM and 400 RPM) two ormore injections are supplied to each engine cylinder during thecompression stroke of each cylinder receiving the fuel. At intermediateengine speeds (e.g., between 400 RPM and 700 RPM), multiple fuelinjections are supplied during both intake and compression strokes ofeach cylinder receiving the fuel. At higher engine speeds (e.g., 700 RPMto 1000 RPM), multiple fuel injections are supplied solely during theintake stroke of the cylinder receiving the fuel. Of course, the lower,intermediate, and higher engine speeds may differ between applications.For example, the lower engine speed may be between 200 RPM and 300 RPM,the intermediate engine speed may be between 300 RPM and 800 RPM, andthe higher engine speed may be between 800 RPM and 1100 RPM for otherapplications. Thus, if the desired engine speed is a higher enginespeed, the fuel injection timing is adjusted to provide multiple fuelinjections solely during the intake stroke of the cylinder receiving thefuel when the engine reaches the desired engine speed. If the desiredengine speed is an intermediate engine speed the fuel injection timingis adjusted to provide multiple fuel injections during intake andcompression strokes of the cylinder receiving the fuel. The split fuelinjection timing at higher engine speeds provides for improved fuelmixing and reduced engine emissions. The split fuel injection duringcompression and intake strokes provides for improved combustionstability and reduced possibility of engine misfire.

As engine speed increases from cranking speed (e.g., 250 RPM) to thedesired idle speed during engine run-up, the amount of time between endof injection (EOI) (e.g., the timing where the last fuel pulse injectedto a cylinder during a cycle of the cylinder occurs) and sparkinitiation is held substantially constant (e.g., ±3 degrees). Since thetime between different crankshaft positions decreases as engine speedincreases, EOI timing is advanced with respect to crankshaft timing tomaintain a substantially constant amount of time (e.g., ±0.05 seconds)between EOI and spark initiation. Further, when multiple fuel injectionsare performed, timing of each of the fuel injections during a cylindercycle may be advanced as engine speed increases. Thus, start of fuelinjection (SOI) during a cylinder cycle may be advanced as engine speedincreases during engine run-up.

If the desired engine speed is greater than the actual engine speed,fuel injection amounts are increased via increasing fuel injectionduration. Additional air may also be provided to the engine via openingthe throttle. If the desired engine speed is less than the actual enginespeed, fuel injection amounts are decreased via reducing fuel injectionduration. The engine air amount may be reduced via closing the throttle.Further, the fuel injection timing and fuel amounts may be adjusted inresponse to driveline disconnect clutch operating conditions so as topreemptively adjust fuel injection timing. For example, if the drivelinedisconnect clutch is closing and the engine side of the drivelinedisconnect clutch is rotating slower than the DISG side of the drivelinedisconnect clutch, the fuel injection amount may be increased toaccelerate the engine closer to DISG speed and thereby reduce drivelinetorque disturbances. On the other hand, if the driveline disconnectclutch is closing and the engine side of the driveline disconnect clutchis rotating faster than the DISG side of the driveline disconnectclutch, the fuel injection amount may be decreased to decelerate theengine closer to DISG speed. Further, if the driveline disconnect clutchis being opened, the fuel injection amount may be decreased as afunction of driveline disconnect clutch application force to deceleratethe engine to idle speed and thereby reduce driveline torquedisturbances. Similarly, if the driveline disconnect clutch beingopened, the fuel injection amount may be increased as a function ofdriveline disconnect clutch application force to accelerate the engineto idle speed and thereby reduce driveline torque disturbances.

In some examples, the fuel injection timing of an engine cylinder isadjusted to a stroke of a cylinder that varies as engine speed varies.For example, if a speed differential between actual and desired enginespeed increases, method 1300 adjusts fuel from a compression stroke toan intake stroke. By varying the injection stroke based on a speeddifferential between actual and desired engine speed, it may be possibleto improve air-fuel mixing and promote more complete combustion so thatthe speed differential may be reduced.

Additionally, the engine throttle position may be adjusted in responseto timing of when fuel is injected to a cylinder. For example, a portthrottle may be partially closed to increase charge motion when fuel isinjected solely during an intake stroke. The port throttle may bepartially opened as fuel injection transitions from injecting fuelduring a compression stroke to injecting fuel during an intake stroke.Further, the amount of fuel injected to the cylinder during the cylindercycle is adjusted based on an amount of air that flows through athrottle. Method 1300 proceeds to 1312 after fuel injection timing isadjusted.

At 1312, method 1300 adjusts spark timing in response to the state ofthe driveline disconnect clutch and the speed differential between thedesired engine speed and the actual engine speed. In particular, whenengine speed is substantially at DISG speed (e.g., +100 RPM), the sparkis retarded to a level to produce zero torque at the drivelinedisconnect clutch. Further, the spark retard may also be provided basedon the speed difference between the DISG and the engine. As the speeddifferential between the engine and the DISG is reduced, the amount ofspark retard is increased.

At 1314, method 1300 judges whether or not the driveline disconnectclutch has been closed to a threshold amount (e.g., 80% of clutchholding torque is provided). The driveline disconnect clutch may beclosed when the engine speed is within a predetermined speed of thetorque converter impeller speed so that torque disturbances though thedriveline may be reduced. If method 1300 judges that the drivelinedisconnect clutch has been closed to a threshold amount, method 1300proceeds to 1316. Otherwise, method 1300 returns to 1304.

At 1316, method 1300 advances spark timing and transitions to injectionof fuel in a single fuel injection during a cycle of a cylinder based ona number of combustion events since engine stop or based on a torqueratio. For example, after the driveline disconnect clutch closes, method1300 may transition from split fuel injection to single fuel injectionduring a cylinder cycle after 10 combustion events. Alternatively,method 1300 may transition from split fuel injection to single fuelinjection during a cylinder cycle after spark timing has been advancedto timing where a torque ratio between spark timing and fuel injectiontiming is less than a threshold amount. Method 1300 proceeds to exitafter fuel injection timing and spark timing are transitioned to basetimings that are empirically determined and stored in memory.

Referring now to FIG. 14, a plot of an example sequence for supplyingfuel to an engine according to the method of FIG. 13 is shown. Thesequence of FIG. 14 may be provided by the system of FIGS. 1-3.

The first plot from the top of FIG. 14 represents fuel injection timingfor cylinder number one. The X axis represents cylinder stroke forcylinder number one and individual cylinder strokes are indicated byrepresentative letters. For example, intake stroke is represented by I,compression stroke is represented by C, power stroke is represented byP, and exhaust stroke is represented by E. The Y axis represents fuelinjection.

The second plot from the top of FIG. 14 represents desired torqueconverter impeller speed versus cylinder number one stroke. The X axistiming is coincident with the timing of the first plot from the top ofthe figure. The Y axis represents desired torque converter impellerspeed and desired torque converter impeller speed increases in thedirection of the Y axis arrow.

The third plot from the top of FIG. 14 represents desired engine speedversus cylinder number one stroke. The X axis timing is coincident withthe timing of the first plot from the top of the figure. The Y axisrepresents desired engine speed and desired engine speed increases inthe direction of the Y axis arrow.

The fourth plot from the top of FIG. 14 represents actual engine speedversus cylinder number one stroke. The X axis timing is coincident withthe timing of the first plot from the top of the figure. The Y axisrepresents actual engine speed and actual engine speed increases in thedirection of the Y axis arrow.

The fifth plot from the top of FIG. 14 represents a difference betweendesired engine speed and actual engine speed (delta engine speed) versuscylinder number one stroke. The X axis timing is coincident with thetiming of the first plot from the top of the figure. The Y axisrepresents desired engine speed and desired engine speed increases inthe direction of the Y axis arrow.

At time T₁₈, the engine is stopped and the desired torque converterimpeller speed is zero. The engine rotates after T₁₈ cycling through thedifferent stroke of cylinder number one. A first single fuel injectionamount is delivered directly to cylinder number one during thecompression stroke of cylinder number one. The engine begins toaccelerate from a first combustion event during the first compressionstroke since engine stop.

At time T₁₉, two fuel injections are provided during the secondcompression stroke of cylinder number one. The fuel injectiontransitions to two injections in response to a speed difference betweenthe desired engine speed and the actual engine speed. Further, the fuelinjection is delivered during a cylinder stroke that depends on thespeed difference between actual and desired engine speeds. In oneexample, fuel injection timing for cylinder stroke based on thedifference between actual and desired engine speed is stored in a tableand outputs a cylinder stroke based on the speed difference. Byadjusting the cylinder stroke where fuel injection occurs based on adifference between actual and desired engine speed, it may be possibleto improve fuel mixing and engine speed control during engine starting.

Between time T₁₉ and time T₂₀, fuel injection timing is adjusted furtherin response to the difference in desired engine speed and actual enginespeed. It may be observed that fuel injection changes from injectingfuel twice during a compression stroke of the cylinder to injecting fuelonce during and intake stroke and once during a compression stroke.Further, fuel injection transitions to injecting fuel twice during anintake stroke.

At time T₂₀, the engine speed error between desired engine speed andactual engine speed goes to zero and fuel is injected once per cylindercycle. In this way, the fuel injection timing may be adjusted to deliverfuel during different engine strokes in response to engine speed error.Further, fuel injection timing and spark timing may be adjustedresponsive to driveline disconnect clutch state or applied force asdiscussed with reference to FIG. 13.

The methods and systems of FIGS. 1-3 and 13-14 also provide foradjusting cylinder air charge of an engine, comprising: positioning athrottle for an engine start; and adjusting a fuel injection timing of acylinder to a stroke of the cylinder that varies as a difference betweena desired engine speed and an actual engine speed varies and adjustingan amount of fuel supplied to the cylinder in response to an amount ofair passing the throttle. The method includes where the stroke of thecylinder varies from a compression stroke to an intake stroke. Themethod includes where the throttle is a port throttle.

In some examples, the method further comprises where the port throttleis at least partially closed during fuel injection during a compressionstroke. The method further comprises where the port throttle is openduring fuel injection during an intake stroke of the cylinder. Themethod also includes where the fuel injection timing provides at leasttwo fuel injections during a cycle of the cylinder. The method includeswhere the fuel injection timing is supplied to a fuel injector thatinjects fuel directly into the cylinder.

The methods and systems of FIGS. 1-3 and 13-14 also provide foradjusting cylinder air charge of an engine, comprising: positioning athrottle for an engine start; providing a spark to a combustion chamberof a cylinder during a cycle of the cylinder; and adjusting a fuelinjection timing to maintain a substantially constant amount of timebetween the spark and an end of fuel injection time as engine speedincreases during engine run-up while injecting a plurality of fuelpulses during the cycle of the cylinder; and adjusting an amount of fuelsupplied to the cylinder in response to an amount of air passing thethrottle. In this way, combustion consistency may be maintained.

The method also includes where the fuel injection timing is advanced asengine speed increases. The method further comprises where the fuelinjection timing is responsive to a desired engine speed, and where thedesire engine speed is based on a torque converter impeller speed. Themethod further comprises closing a driveline disconnect clutch whenengine speed is within a threshold speed of the torque converterimpeller speed. The method includes where a cylinder stroke during whichthe plurality of fuel pulses are injected varies as engine speed varies.The method further comprises where the spark timing is varied duringengine run-up. The method includes where the throttle is a port throttlelocated downstream of an intake manifold.

The methods and systems of FIGS. 1-3 and 13-14 also include a hybridvehicle system, comprising: an engine; a dual mass flywheel (DMF)including a first side mechanically coupled to the engine; a drivelinedisconnect clutch including a first side coupled to a second side of thedual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; and a controller including non-transitoryinstructions executable to adjust fuel injection timing to a cylinder inresponse to a desired engine speed that is based on a torque converterimpeller speed while the torque converter impeller is not mechanicallycoupled to the engine. By adjusting fuel injection timing based ontorque converter impeller speed it may be possible to adjust fuelinjection timing so that desired fuel injection timing is provided whenthe engine reaches the torque converter impeller speed. Such operationmay improve engine emissions.

The hybrid vehicle system further comprises additional instructions toclose the driveline disconnect clutch after engine speed is within athreshold speed of the torque converter impeller speed. The hybridvehicle system includes where the engine is started by rotating theengine via a starter other than the DISG. The hybrid vehicle systemfurther comprises additional instructions to adjusting the fuelinjection timing to maintain a substantially constant amount of timebetween timing of a spark delivered to a cylinder and timing of end offuel injection delivered to the cylinder during a cycle of the cylinderas engine speed increases during engine run-up and while injecting aplurality of fuel pulses during the cycle of the cylinder. The hybridvehicle system also further comprises additional instructions to adjustthe fuel injection timing of a cylinder to a stroke of the cylinder thatvaries as a difference between the desired engine speed and an actualengine speed varies and adjusting an amount of fuel supplied to thecylinder in response to an amount of air passing the throttle. Thehybrid vehicle system further comprises additional instructions toinject a single pulse of fuel to the cylinder during a compressionstroke of the cylinder before a first combustion event of the cylindersince engine stop.

Referring now to FIG. 15, a flowchart of a method for starting an enginewhen torque provided via an electric machine may not provide a desiredamount of torque after a transmission gear shift is shown. The method ofFIG. 15 may be stored as executable instructions in non-transitorymemory of controller 12 in FIGS. 1-3.

At 1502, method 1500 judges whether or not a transmission upshift isdesired or commanded. In one example, a transmission upshift command maybe determined via monitoring status of a control variable that changesstate in response to vehicle speed, demand torque, and gear presentlyselected. If the control variable indicates that a transmission shift isdesired, method 1500 proceeds to 1506. Otherwise, method 1500 proceedsto 1504.

At 1504, method 1500 determines transmission output shaft speed andtorque converter impeller speed for a next impending transmission shiftbased on desired torque. In one example, the desired torque provided viaan accelerator pedal, present selected transmission gear, and vehiclespeed are the basis for determining transmission output speed andimpeller speed for a next transmission upshift. In particular,transmission output speed and next gear may be determined from thepresent gear selected and the vehicle speed at which the transmission isscheduled to upshift to the next gear at a desired engine torque level.A shift schedule may be empirically determined and stored in memorywhich outputs which gear is selected at a present vehicle speed at adesired torque level. Vehicle speed can be extrapolated to a future timebased on the present vehicle speed and the rate of change or slope ofthe vehicle speed according to the equation y=m×+b where y is theprojected vehicle speed, m is the vehicle speed slope, and b is thevehicle speed offset. Similarly, the desired impeller speed can beextrapolated to a future time. As the extrapolation time increases(e.g., present time plus 0.2 seconds, and assuming an increasing vehiclespeed and/or desired torque) from the present time, the shift schedulemay command an upshift to a higher gear (e.g., from 1^(st) gear to2^(nd) gear) as variables that index the shift schedule change. Theextrapolated amount of time when the transmission shift occurs (e.g.,the projected shift time) as well as the new gear number, theextrapolated vehicle speed, and the extrapolated desired torque arestored in memory when the selected transmission gear changes accordingto the shift schedule. The transmission output shaft speed is determinedfrom the new gear (e.g., the upshift gear), any axle ratio, and vehiclespeed. The transmission impeller speed may be predicted from the DISGspeed since the DISG is mechanically coupled to the impeller. Method1500 proceeds to 1506 after the, transmission impeller speed andtransmission output shaft speed are determined.

At 1506, method 1500 determines transmission speeds (e.g., impellerspeed and output shaft speed) and gear ratios for the torque demand inthe next transmission upshift gear. In one example, method 1500determines transmission output shaft speed based on the followingequations:

OSS=OSS_when_commanded+OSS_rateofchange*time_to_shift;

Commanded_gear=gearfn(vs,dsd _(—) tor);

TSS_after_upshift=OSS*Commanded_gear;

Where OSS is transmission output shaft speed, OSS_when_commanded istransmission output shaft speed when the upshift is commanded,time_to_shift is the amount of time it takes for a shift, Commanded_gearis the gear active after the upshift, gearfn is a function that returnscommanded gear, vs is vehicle speed, dsd_tor is desired transmissioninput torque, and TSS_after_upshift is transmission output shaft speedafter upshift. The function fn holds empirically determined gears withwhich the transmission operates. Method 1500 proceeds to 1508 aftertransmission speeds and gear ratio after the shift are determined.

At 1508, method 1500 determines desired transmission output shaft torqueand transmission turbine shaft torque after an upshift. In one example,method 1500 determines transmission output torque and turbine shafttorque based on the following equations:

OUTq _(—) dsd=outfn(accel_pedal,TSS_after_upshift);

Turq_(—) dsd=OUTq _(—) dsd*mult+offset;

Where OUTq_dsd is desired transmission output shaft torque, outfn is afunction that returns desired transmission output shaft torque,accel_pedal is accelerator pedal position which provides a desiredtorque, TSS_after_upshift is transmission output shaft speed afterupshift, Turq_dsd is desired transmission turbine shaft torque, mult andoffset are empirically determined parameters stored in functions that isindexed via commanded gear, transmission oil temperature, andtransmission output shaft speed. Method 1500 proceeds to 1510 afterdesired transmission output shaft torque and transmission turbine shafttorque following the upshift are determined.

At 1510, method 1500 judges whether or not the torque converter clutch(TCC) will be open after an upshift. In one example, method 1500 judgeswhether or not the TCC will be open after an upshift based in anempirically determined shift schedule that is stored in memory. Forexample, based on the present gear, the next scheduled gear, and thedesired torque, the shift schedule may schedule a closed torqueconverter. If method 1500 judges that the TCC will be open after theupshift, the answer is yes and method 1500 proceeds to 1512. Otherwise,the answer is no and method 1500 proceeds to 1514.

At 1512, method 1500 determines demanded torque converter impellertorque. In one example, the demanded torque converter impeller torque isretrieved from a table stored in memory. The table contains empiricallydetermined values of torque converter impeller torque that are indexedvia transmission output shaft speed after upshift and desired turbineshaft torque. Method 1500 proceeds to 1516 after demanded impellertorque is determined.

At 1514, method 1500 adjusts desired torque converter impeller torque todesired torque converter turbine torque since the TCC is in a lockedstate. Method 1500 proceeds to 1516 after desired torque converterimpeller torque is determined.

At 1516, method 1500 judges whether or not the desired torque converterimpeller torque following the transmission upshift will require theengine to be combusting an air-fuel mixture. In one example, method 1500compares an amount of torque the DISG has the capacity to provide at thepresent state of battery charge to the desired torque converter impellertorque. If the desired torque converter impeller torque is greater thanor within a threshold torque amount of the DISG torque capacity theanswer is yes and method 1500 proceeds to 1520. Otherwise, the answer isno and method 1500 proceeds to 1518.

At 1518, method 1500 may allow the engine to stop rotating based onpresent operating conditions or method 1500 may allow the engine tocontinue to combust an air-fuel mixture. In one example, where theengine has reached warm operating conditions, the engine stops rotatingsince the desired torque converter impeller torque does not requireengine operation. The engine may continue to combust when the engine hasnot reached warm operating conditions. Method 1500 proceeds to exitafter engine rotation is allowed or inhibited based on operatingconditions not related to the transmission shift.

At 1520, method 1500 judges whether or not to start the engine beforeupshifting the transmission. The engine may be started before the statesof transmission clutches (e.g., not including the driveline disconnectclutch 236) are adjusted so that engine torque may be transmitted to thevehicle wheels at the end of the gear upshift. Alternatively, the enginemay be started during the upshift at a time when one or moretransmission clutches are changing operating state. In one example, theengine may be started before engine upshift begins and beforetransmission clutches begin to change state when it is expected to takethe engine a longer amount of time to produce positive torque than thetime expected to shift gears. If method 1500 judges that it is desirableto start the engine before the transmission upshift, method 1500proceeds to 1522. Otherwise, method 1500 proceeds to 1526.

At 1522, method 1500 starts the engine and engages the drivelinedisconnect clutch. The engine may be started via rotating the engine viaa starter motor that has a lower power output capacity than the DISG orvia cranking the engine via the DISG. Further, the transmission shiftmay be delayed until the engine speed is synchronous with the DISG orimpeller speed. Delaying the transmission shift can reduce drivelinetorque disturbance that may occur if the engine torque increases beforethe off-going clutch is completely released. Method 1500 proceeds to1524 after the engine is started and the driveline disconnect clutch isreleased.

At 1524, method 1500 upshifts the transmission after the drivelinedisconnect clutch is engaged. The transmission may be upshifted viaapplying and/or releasing pressure to one or more clutches that affecttorque transfer through the transmission. Method 1500 exits after thetransmission is shifted.

At 1526, method 1500 inhibits engine stopping if conditions other thanthe impending transmission upshift are present for stopping enginerotation. In other words, if the engine would be commanded to stop butfor upshifting the transmission, then stopping engine rotation of thetransmission is inhibited. Additionally, the engine may be started at atime after the upshift has commenced (e.g., during release of theoff-going clutch (torque phase) or during application of the on-comingclutch (inertia phase)) to provide additional torque to the driveline tomeet the torque request. Engine and DISG torque may be adjusted toprovide the desired amount of torque converter impeller torque. Method1500 proceeds to exit after engine stopping is inhibited or after theengine is started after upshifting the transmission commences.

In this way, method 1500 can forecast transmission shifting and desiredtorque converter impeller torque to determine when to closed thedriveline disconnect clutch and start the engine. Method 1500 may allowengine torque to be seamlessly combined with DISG torque to providesmooth acceleration during transmission shifting.

Referring now to FIG. 16, a plot of an example sequence for determiningwhen to start an engine according to the method of FIG. 15 is shown. Thesequence of FIG. 16 may be provided by the system of FIGS. 1-3.

The first plot from the top of FIG. 16 represents desired drivelinetorque versus time. Desired driveline torque may be a desired torqueconverter impeller torque, a desired torque converter turbine torque,desired wheel torque, or other driveline torque. The desired drivelinetorque may be determined from an accelerator pedal position or otherinput device. Solid trace 1602 represents desired driveline torque.Dashed trace 1604 represents forecasted desired driveline torque (e.g.,desired driveline torque after a transmission gear shift). The Y axisrepresents desired driveline torque and desired driveline torqueincreases in the direction of the Y axis. The X axis represents time andtime increases from the left hand side of the figure to the right handside of the figure. Horizontal line 1606 represents a limit of torquethat may be supplied to the driveline via the DISG.

The second plot from the top of FIG. 16 represents transmission gearversus time. The Y axis represents transmission gear and specifictransmission gears are indicated along the Y axis. The X axis representstime and time increases from the left hand side of the figure to theright hand side of the figure. Solid trace 1608 represents the presentor actual transmission gear. Dashed trace 1610 represents the forecastedor future transmission gear.

The third plot from the top of FIG. 16 represents desired engine stateabsent transmission gear shifting conditions versus time. The Y axisrepresents desired engine state and desired engine state is on forhigher trace levels and off for lower trace levels. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The fourth plot from the top of FIG. 16 represents desired engine statebased on all conditions versus time. The Y axis represents desiredengine state and desired engine state is on for higher trace levels andoff for lower trace levels. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The fifth plot from the top of FIG. 16 represents engine state versustime. The Y axis represents engine state and engine state is on forhigher trace levels and off for lower trace levels. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

At time T₂₁, the desired driveline torque is greater than an amount oftorque that may be provided by the DISG to the driveline. Thetransmission is in 5^(th) gear and the desired engine state and thedesired engine state absent gear conditions are both at higher levelsindicating that the engine is desired to be operating. The engine stateis at a higher level indicating that the engine is operating

Between time T₂₁ and time T₂₂, the desired driveline torque decreases inresponse to a decreasing driver input (not shown). The transmissiondownshifts from 5^(th) to 2^(nd) gear and the forecasted transmissiongear leads the present or actual transmission gear. The desired enginestate absent gear conditions and the desired engine state remain athigher levels.

At time T₂₂, the desired transmission state absent gear conditionstransitions to a lower level in response to vehicle speed and desireddriveline torque to indicate that the engine may be stopped but fortransmission gear conditions in response to vehicle and engine operatingconditions (e.g., brake applied, accelerator pedal not applied, andvehicle speed less than a threshold speed). The desired engine statealso transitions to a lower level to indicate to stop the engine inresponse to operating conditions including the forecasted transmissiongear. The engine is stopped in response to the desired engine state.

Between time T₂₂ and time T₂₃, the desired driveline torque levels outand then increases. The forecasted transmission gear increases from2^(nd) gear to 3^(rd) gear as the desired driveline torque increases.The present transmission gear is held in 2^(nd) gear. The engine remainsstopped since the desired engine state and the desired engine stateabsent gear conditions remain at a lower level.

At time T₂₃, the desired engine state transitions to a higher level inresponse to the forecasted desired driveline torque increasing after theshift to a level greater than 1606. The engine is started in response tothe transition of the desired engine state. The desired engine stateabsent gear conditions remains at a lower level to indicate that theengine would remain off but for the increase in desired driveline torqueexpected after the transmission shift.

Between time T₂₃ and time T₂₄, the desired driveline torque increasesand then decreases in response to a reduced driver demand (not shown).The desired driveline torque decreases to a level less than 1606 andholds near level 1606. The transmission downshifts to 3^(rd) gear from5^(th) gear. The desired engine state and the desired engine stateabsent gear conditions remain at higher levels so that the engineremains on.

At time T₂₄, the desired engine state absent gear conditions transitionsto a lower level to indicate that the engine may be stopped in responseto the desired driveline torque, vehicle speed (not shown), and brakeapplied (not shown). However, the desired engine state remains at a highlevel in response to the forecasted desired driveline torque increasingto a level greater than 1606 as forecast for the transmission shiftingto 4^(th) gear. Consequently, engine stopping is inhibited. Suchconditions may be present when a vehicle is moving and when a drivertips-out (e.g., releases or reduces) an accelerator pedal command.

Between time T₂₄ and time T₂₅, the desired driveline torque increasesand then decreases. The transmission shifts gears between 3^(rd) and5^(th) gears in response to driver demand torque, vehicle speed (notshown), and brake state (not shown). The desired engine state absentgear conditions and the desired engine state remain at higher levels inresponse to the desired driveline torque.

At time T₂₅, the desire driveline torque is reduced to less than level1606 in response to a lower driver demand (not shown). The desiredengine state absent gear conditions and the desired engine statetransition to a lower level to indicate the engine is to be stopped inresponse to the desired driveline torque, brake pedal state (not shown),and vehicle speed (not shown). The engine is stopped in response to thedesired engine state.

Between time T₂₅ and time T₂₆, the desired driveline torque graduallyincreases and the forecast transmission gear increases from 2^(nd) gearto 3^(rd) gear in response to the increasing desired driveline torque.The desired engine state and the desired engine state absent gearconditions remain at a lower level and the engine remains stopped.

At time T₂₆, the desired engine state transitions to a higher level andthe engine is started in response to the increasing desired drivelinetorque and the forecasted transmission gear. The desired engine stateabsent gear conditions remains at a low level indicating that the enginewould not be started but for the forecasted desired driveline torquebeing greater than 1606 after a forecasted transmission gear shift. Bystarting the engine before the actual gear shift, it may be possible toprovide the desired driveline torque after a shift.

In this way, the engine may be started before a gear shift to provide adesired driveline torque after the gear shift. Further, the methodforecasts shifting so that the engine may be started before the desireddriveline torque is actually requested. Starting the engine early mayallow the engine to reach conditions where it may output torque to meetthe desired driveline torque.

The methods and systems of FIGS. 1-3 and 15-16 provide for a method ofstarting an engine, comprising: predicting a desired torque after atransmission upshift; and starting rotation of a stopped engine if thepredicted desired torque after the transmission upshift is greater thana threshold amount of torque. The method includes where the desiredtorque is a torque converter impeller torque, and where the predictingthe desired torque and starting rotation are during conditions where adriveline integrated starter/generator is providing torque to wheels andwhere the transmission is in a forward gear and where the vehicle ismoving. The method includes where the desired torque is predicted basedon a predetermined transmission shift schedule.

In some examples, the method includes where rotation of the engine isstarted via a driveline disconnect clutch. The method includes where thedriveline disconnect clutch is disengaged prior to rotating the engine.The method includes where the driveline disconnect clutch is located inthe hybrid vehicle driveline between a dual mass flywheel and adriveline integrated starter/generator. The method includes where theengine is rotated in response to the predicted desired driveline torquebefore a transmission is shifted.

The methods and systems of FIGS. 1-3 and 15-16 provide for starting anengine, comprising: providing a torque to a vehicle driveline via anelectric machine; scheduling a transmission upshift; and startingrotation of a stopped engine in response to the scheduled transmissionupshift if a desired torque after the scheduled transmission upshift isgreater than a threshold amount of torque, and where the desired torqueis based on driveline integrated starter/generator torque after atransmission upshift timing of engaging a transmission clutch relativeto starting the engine. The method includes where the electric machineis a driveline integrated starter/generator (DISG) and where the DISG islocated in the hybrid vehicle driveline at a location between adriveline disconnect clutch and a transmission.

In some examples, the method includes where the DISG provides torque tostart rotation of the stopped engine via at least partially closing thedriveline disconnect clutch. The method further comprises upshifting thetransmission after starting rotation of the engine. The method alsoincludes where the transmission is a dual layshaft—dual clutchtransmission. The method includes where the transmission is an automatictransmission. The method further comprises allowing the engine to stoprotating if the desired torque after the transmission upshift timing ofengaging a transmission clutch relative to starting the engine is lessthan the threshold amount of torque.

The methods and systems of FIGS. 1-3 and 15-16 provide for a hybridvehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generatormechanically including a first side coupled to a second side of thedriveline disconnect clutch; and a controller including non-transitoryinstructions executable to start the engine via closing the drivelinedisconnect clutch in response to a desired torque after a scheduledtransmission upshift, the engine started before the transmission shiftsin response to the scheduled transmission upshift. Such a system mayimprove driveline response time.

In one example, the hybrid vehicle system further comprises additionalinstructions to inhibit stopping engine rotation if the engine isrotating before the scheduled transmission upshift. The hybrid vehiclesystem includes where the engine is started by rotating the engine viathe driveline integrated starter/generator in response to closing thedriveline disconnect clutch. The hybrid vehicle system further comprisesadditional instructions to upshift the transmission after the engine isstarted. The hybrid vehicle system further comprises additionalinstructions to allow the engine to stop rotating in response to thedesired torque after the scheduled transmission upshift. The hybridvehicle system further comprises additional instructions to delaystarting the engine until the scheduled transmission upshift isscheduled for a time less than a threshold amount of time.

Referring now to FIG. 17, a flowchart of a method for starting an engineto reduce transmission input torque during a transmission shift isshown. The method of FIG. 17 may be stored as executable instructions innon-transitory memory in the system shown in FIGS. 1-3. The method ofFIG. 17 may reduce the magnitude and/or number of times torque changesare made to a DISG during vehicle operation to limit torque applied to atransmission during transmission shifting.

At 1702, method 1700 judges whether or not an engine restart andtransmission upshift are desired. An engine restart may be requestedwhen a requested driveline torque is increased or when a driver releasesa brake pedal, for example. A transmission upshift may be requested inresponse to vehicle speed and driveline torque demand, for example. Inone example, a transmission shifting schedule is empirically determinedand stored in memory to be indexed by vehicle speed and driveline torquedemand. If method 1700 determines that a transmission upshift and enginestart are requested, method 1700 proceeds to 1704. Otherwise, method1700 proceeds to exit.

At 1704, method 1700 judges whether or not the DISG is available. Method1700 may judge whether or not the DISG is available based on a DISGstate flag stored in memory. Alternatively, method 1700 may judgewhether or not a DISG is available based on operating conditions such asbattery state of charge. For example, if SOC is less than a thresholdlevel, the DISG may not be available. In another example, the DISG maynot be available if DISG temperature is greater than a threshold. Ifmethod 1700 judges that the DISG is available the answer is yes andmethod 1700 proceeds to 1712. Otherwise, the answer is no and method1700 proceeds to 1706.

At 1706, method 1700 releases an off-going clutch at a scheduled rate.The off-going clutch is a lower gear during an upshift. For example, theoff-going clutch releases a 2^(nd) gear clutch during a 2^(nd) to 3^(rd)gear upshift. The clutch release rate may be empirically determined andstored in memory so that when the upshift occurs the off-going clutchcan be released at a rate that is stored in memory. The off-going clutchmay be released via lowering oil pressure supplied to the off-goingclutch. Method 1700 proceeds to 1708 after the off-going clutch isreleased.

At 1708, method 1700 begins to apply the on-coming clutch to engage ahigher gear after a predetermined amount of time since release of theoff-going clutch commenced. The on-coming clutch may be applied byincreasing pressure of oil supplied to the on-coming clutch. Thepredetermined amount of time may be empirically determined and stored inmemory for use during an upshift. In one example, the on-coming clutchis applied at a time that reduces the possibility of wearing of theoff-going clutch by speeding up the output side of the off-going clutch.Method 1700 proceeds to 1710 after application of the on-coming clutchis initiated.

At 1710, method 1700 applies or begins to close the driveline disconnectclutch at a controlled rate to reduce transmission input shaft torque.In particular, the engine applies a load to the input side of the torqueconverter by closing the driveline disconnect clutch so as to reduce thespeed of the torque converter impeller speed. In this way, the amount oftorque transmitted through the torque converter to the transmissioninput shaft is decreased. In one example, the driveline disconnectclutch rate is adjusted based on the torque converter impeller speed asthe driveline disconnect clutch is applied. For example, the drivelinedisconnect clutch application pressure is increased until torqueconverter impeller speed is reduced to a threshold amount and then thedriveline disconnect clutch application pressure is not furtherincreased. Since the driveline disconnect clutch transfers torque fromthe input side of the transmission to the engine, the amount of torquetransferred to the engine from the transmission is limited based on theimpeller speed. Method 1700 proceeds to 1722 after the drivelinedisconnect clutch application pressure is increased and the drivelinedisconnect clutch is at least partially closed.

At 1712, method 1700 releases an off-going clutch at a scheduled rate.Releasing the off-going clutch allows a higher gear to be appliedwithout torque being transferred via two different gears. The off-goingclutch release rate may be empirically determined and stored in memoryfor retrieval during upshifting. Method 1700 proceeds to 1714 afterrelease of the off-going clutch is initiated.

At 1714, method 1700 increases DISG output torque to increase the torquesupplied to the torque converter impeller. In one example, the DISGtorque is increased by an amount of torque used to accelerate the engineto a desire engine speed. The DISG torque may be increased viaincreasing an amount of current supplied to the DISG. In other examples,the DISG output torque may be reduced to lower transmission inputtorque. Method 1700 proceeds to 1716 after DISG torque is increased.

At 1716, method 1700 begins to apply the on-coming clutch to engage ahigher gear after a predetermined amount of time since release of theoff-going clutch commenced. The on-coming clutch may be applied byincreasing pressure of oil supplied to the on-coming clutch. Thepredetermined amount of time may be empirically determined and stored inmemory for use during an upshift. In one example, the on-coming clutchis applied at a time that reduces the possibility of wearing of theoff-going clutch by speeding up the output side of the off-going clutch.Method 1700 proceeds to 1718 after application of the on-coming clutchis initiated.

At 1718, method 1700 applies or begins to close the driveline disconnectclutch at a controlled rate to reduce transmission input torque andaccelerate the engine to a desired cranking speed. In particular, theengine applies a load to the input side of the torque converter byclosing the driveline disconnect clutch so as to reduce the speed of thetorque converter impeller. The driveline disconnect clutch applypressure may be modulated to control the torque transfer across thedriveline disconnect clutch. Further, the driveline disconnect clutchmay be applied any time during the inertia phase of shifting when theon-coming clutch is being closed.

In one example, the driveline disconnect clutch application rate may beadjusted based on the torque converter impeller speed as the drivelinedisconnect clutch is applied. Since the driveline disconnect clutchtransfers torque from the input side of the transmission to the engine,the amount of torque transferred to the engine is limited based on theimpeller speed. In another example, a transfer function of the drivelinedisconnect clutch that relates torque transferred based on the amount ofinput torque supplied to the driveline disconnect clutch and drivelinedisconnect clutch apply pressure is multiplied by the DISG torque todetermine an amount of torque transferred to the engine to start theengine. The driveline disconnect clutch application rate may be adjustedsuch that a desired cranking torque is provided to the engine via theDISG and driveline disconnect clutch.

In still another example, the driveline disconnect clutch applicationrate may be controlled based on speed of the DISG and a desired enginespeed run-up rate. For example, a driveline disconnect clutchapplication rate may be retrieved from an empirically determined tablethat outputs driveline disconnect clutch application rate when indexedvia DISG speed and desired engine acceleration. Method 1700 proceeds to1720 after driveline disconnect clutch application is initiated.

At 1720, method 1700 adjusts DISG torque to provide a desiredtransmission input torque via the torque converter impeller during orafter the inertia phase of the transmission upshift. If the engine massis relatively high, DISG output may be increased so that thetransmission input torque is not reduced more than is desired. If theengine mass is relatively low, the DISG torque may be reduced so thattransmission input torque is reduced by a desired amount. The DISGtorque may be adjusted by increasing or decreasing current supplied tothe DISG. Method 1700 proceeds to 1722 after DISG torque is adjusted.

At 1722, method 1700 starts the engine when engine speed reaches athreshold speed by supplying fuel and spark to the engine. In someexamples, a starter other than the DISG may be engaged to the engine toprovide torque additional to the torque provided by the drivelinedisconnect clutch to the engine when the engine is being started so thata desired engine cranking speed may be achieved. Method 1700 proceeds toexit after the engine is started.

In this way, transmission output shaft torque may be reduced during aninertia phase of shifting so that driveline torque disturbances may bereduced. Starting the engine via closing the driveline disconnect clutchreduces the transmission input shaft torque so that the transmissionoutput shaft torque may be reduced during the inertia phase of shifting.

Referring now to FIG. 18, an example sequence of starting an engineduring transmission gear shifting according to the method of FIG. 17 isshown. The sequence of FIG. 18 may be provided by the system of FIGS.1-3. The dashed traces are equivalent to the solid traces when thedashed traces are not visible.

The first plot from the top of FIG. 18 represents transmission inputshaft torque versus time. The torque at the transmission input shaft isequal to transmission torque converter turbine torque. The Y axisrepresents transmission input shaft torque and transmission input shafttorque increases in the direction of the Y axis. The X axis representstime and time increases from the left hand side of the figure to theright hand side of the figure. Solid trace 1802 represents transmissioninput shaft torque without starting the engine via closing the drivelinedisconnect clutch or providing transmission input shaft torquereduction. Dashed trace 1804 represents the transmission input shafttorque when starting the engine via closing the driveline disconnectclutch and shifting to a higher gear.

The second plot from the top of FIG. 18 represents transmission outputshaft torque versus time. The Y axis represents transmission outputshaft torque and transmission output shaft torque increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure. Solid trace 1806 represents transmission output shafttorque without starting the engine via closing the driveline disconnectclutch or providing transmission input shaft torque reduction. Dashedtrace 1808 represents the transmission output shaft torque when startingthe engine via closing the driveline disconnect clutch and shifting to ahigher gear.

The third plot from the top of FIG. 18 represents driveline disconnectclutch state versus time. The Y axis represents driveline disconnectclutch state where the driveline disconnect clutch is open near the Xaxis and closed near the top of the Y axis. The amount of torquetransferred through the driveline disconnect clutch increases as thedriveline disconnect clutch is closed. The X axis represents time andtime increases from the left hand side of the figure to the right handside of the figure.

The fourth plot from the top of FIG. 18 represents engine speed versustime. The Y axis represents engine speed and engine speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The fifth plot from the top of FIG. 18 represents DISG torque versustime. The Y axis represents DISG torque and DISG torque increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

At time T₂₇, the transmission is not shifting and the engine is stopped.The DISG is outputting torque to the driveline and transmission inputshaft and output shaft torques are constant.

At time T₂₈, the transmission begins to shift in response to atransmission shift schedule, desired driveline torque (not shown), andvehicle speed (not shown). The shift begins by releasing an off-goingclutch. For example, during an upshift from 2^(nd) gear to 3^(rd) gear,the 2^(nd) gear clutch (off-going clutch) releases before the 3^(rd)gear (on-coming clutch) is applied. The transmission input shaft torqueis held constant, although it may be increased in some examples tobetter maintain transmission output shaft torque. The transmissionoutput torque begins to decrease in response to releasing the off-goingclutch. The driveline disconnect clutch is shown being open and theengine is stopped. The DISG torque is shown being maintained at aconstant value.

At time T₂₉, the inertia phase begins by applying the on-coming clutchin response to releasing the off-going clutch. The driveline disconnectclutch begins to close as the on-coming clutch is applied and begins toclose. The transmission input shaft torque is also shown decreasing inresponse to the driveline disconnect clutch closing since some DISGtorque is transferred via the driveline disconnect clutch to rotate theengine. The engine speed begins to increase in response to drivelinetorque being applied to the engine. The DISG torque is shown at aconstant level.

Between time T₂₉ and time T₃₀, the driveline disconnect clutch state isshown being modulated to control the amount of driveline torque beingapplied to the engine. The driveline disconnect clutch apply pressuremay be modulated in response to engine speed and/or transmission outputshaft speed so as to reduce driveline torque disturbances duringshifting and engine starting. Spark and fuel (not shown) are alsosupplied to the engine so that engine speed approaches DISG speed. Thetransmission output shaft torque gradually increases when the drivelinedisconnect clutch is applied to restart the engine as indicated bydashed line 1808. If the driveline disconnect clutch is not appliedduring the inertia phase, the transmission output shaft torque increasesin response to the gear ratio change. Thus, applying the drivelinedisconnect clutch during the inertia phase may reduce driveline torquedisturbances.

At time T₃₀, the inertia phase of transmission shifting is complete asthe on-coming clutch (not shown) is fully applied as indicated by thetransmission output torque converging to a constant value. The DISGtorque is also shown increasing in response to completion of the shiftso that vehicle acceleration may resume.

In this way, a driveline torque disturbance during shifting may bereduced. Further, energy in the driveline may be applied to start theengine so that the DISG may supply less torque to start the engine.

The methods and systems of FIGS. 1-3 and 17-18 provide for shifting atransmission, comprising: coupling an engine to a transmission inresponse to a request to upshift the transmission. In this way,transmission input shaft torque can be reduced to control transmissionoutput shaft torque during a shift. The method includes where the engineis not coupled to the transmission prior to the request to upshift thetransmission, where the transmission is in a moving vehicle and in aforward drive gear, and where the vehicle continues to move and wherethe transmission is upshifted to a higher gear. The method includeswhere the engine is coupled to the transmission via a drivelinedisconnect clutch positioned in a driveline between the engine and atorque converter.

In some examples, the method includes where the engine is coupled to thetransmission during an inertia phase of the upshift. The method includeswhere the engine is coupled to the transmission after release of anoff-going clutch is initiated during the upshift. The method furthercomprises starting the engine when engine speed reaches a thresholdspeed. The method includes where the transmission is an automatictransmission, and where input torque to the automatic transmission isreduced during the upshift.

The methods and systems of FIGS. 1-3 and 17-18 also provide for shiftinga transmission, comprising: reducing input torque to a transmission inresponse to a transmission upshift request via selectively coupling anengine to an input shaft of the transmission, the engine not coupled tothe transmission prior to the transmission upshift request. The methodincludes where the engine is coupled to the transmission via a drivelinedisconnect clutch. The method further comprises a torque converter in adriveline positioned between the engine and the transmission. The methodfurther comprises increasing or decreasing torque of a drivelineintegrated starter/generator during the upshift. The method includeswhere torque from the driveline integrated starter/generator isincreased to hold an impeller speed of a torque converter greater than athreshold speed. The method includes where engine rotation is stoppedprior to the transmission upshift request.

The methods and systems of FIGS. 1-3 and 17-18 also provide for a hybridvehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch and a second side; a transmission coupled to the DISG;and a controller including non-transitory instructions executable toinitiate a transmission shift request and to couple the engine to thetransmission in response to the transmission shift request.

In some examples, the hybrid vehicle system further comprises a torqueconverter located in a driveline between the transmission and the DISG.The hybrid vehicle system further comprises additional instructions tostart the engine. The hybrid vehicle system further comprisingadditional instructions to couple the engine to the transmission via thedriveline disconnect clutch. The hybrid vehicle system further comprisesadditional instructions to increase DISG torque in response to thetransmission upshift request. The hybrid vehicle system furthercomprises additional instructions to reduce DISG torque in response tothe transmission upshift request. The hybrid vehicle system furthercomprises additional instructions to accelerate the engine to a desiredcranking speed.

Referring now to FIG. 19, a method for improving vehicle drivelineresponse when the driveline includes a dual mass flywheel is shown. Themethod of FIG. 19 may be stored as executable instructions innon-transitory memory of controller 12 shown in FIGS. 1-3.

At 1902, method 1900 determines operating conditions. Operatingconditions may include but are not limited to engine speed, DMF inputand output speeds, requested driveline torque, DISG torque, drivelinedisconnect clutch state, and engine torque. Method 1900 proceeds to 1904after operating conditions are determined.

At 1904, method 1900 determines speed and/or position of the upstream orengine side of the DMF. In alternative examples, the torque on theupstream side of the DMF may be determined. The speed and/or positionmay be determined from a position sensor. Torque may be determined via atorque sensor. Method 1900 proceeds to 1906 after speed and/or positionof the upstream side of the DMF is determined.

At 1906, method 1900 determines speed and/or position downstream or onthe driveline disconnect clutch side of the DMF. Alternatively, thetorque on the downstream side of the DMF may be determined. The speedand/or position at the downstream side of the DMF may be determined viaa position sensor. Torque on the downstream side of the DMF may bedetermined via a torque sensor. Method 1900 proceeds to 1908 after thedownstream side speed and/or position of the DMF is determined.

At 1908, method 1900 determines a speed, position, or torque differencebetween the upstream side of the DMF and the downstream side of the DMF.In one example, the driveline disconnect clutch side of the DMF is adesired speed and/or position side of the DMF. The speed and/or positionon the engine side of the DMF is subtracted from the speed and/orposition of the engine side of the DMF to provide a DMF speed and/orposition error across the DMF. Alternatively, torque on the engine sideof the DMF may be subtracted from torque on the upstream side of the DMFto provide a torque error. In some examples, a difference in aspeed/position between a first side of the DMF and a second side of theDMF during driveline operation is compared to a position of the firstside of the DMF and position of the second side of the DMF when notorque is transferred across the DMF.

In another example, a fast Fourier transform of the DMF upstream anddownstream speed signals may be performed to determine amplitude ormagnitude and frequency of any speed oscillations on the upstream anddownstream sides of the DMF. Method 1900 proceeds to 1910 after thespeed error across the DMF and/or the frequencies and amplitudes ofspeed upstream and downstream of the DMF are determined.

At 1910, method 1900 judges whether the speed and/or position error orthe amplitudes and frequencies on the upstream and downstream sides ofthe DMF are greater than threshold levels. If so, method 1900 proceedsto 1912. Otherwise, method 1900 proceeds to exit.

At 1912, method 1900 judges whether or not driveline operatingconditions are within a first operating window. For example, if theupstream and downstream DMF speed error is greater than a firstthreshold level. In other examples, the torque difference or positiondifference across the DMF may be the basis of determining whether or notthe driveline operating conditions are within a first operating window.In still other examples, the frequencies or frequency amplitudes arecompared to threshold values. If driveline operating conditions arewithin a first operating window, method 1900 proceeds to 1914.Otherwise, method 1900 proceeds to 1916.

At 1914, method 1900 method 1900 modulates the transmission torqueconverter clutch (TCC) to dampen speed and/or torque oscillations acrossthe DMF. The TCC is modulated via varying a duty cycle of TCC commandsignal. In other examples, the frequency of the TCC is adjusted. Theduty cycle of the TCC control command is reduced to increase slip acrossthe torque converter clutch, thereby increasing the dampening of theDMF. However, if the TCC is slipping by a threshold amount when thespeed/position difference is detected across the DMF, the TCC may becommanded to a locked position by increasing the TCC duty cycle command.The amount of TCC adjustment may be based on an error between a desiredvalue and an actual value. For example, the TCC duty cycle may beadjusted based on a difference between upstream and downstream DMFspeeds. Method 1900 proceeds to exit after the TCC is adjusted.

At 1916, method 1900 judges whether or not driveline operatingconditions are within a second operating window. For example, if theupstream and downstream DMF speed error is greater than a secondthreshold level. If driveline operating conditions are within a secondoperating window, method 1900 proceeds to 1918. Otherwise, method 1900proceeds to 1920.

At 1918, method 1900 adjusts slip of the driveline disconnect clutch toadjust dampening across the DMF. In one example, the amount of slipacross the driveline disconnect clutch is increased to increasedampening across the DMF. However, if the driveline disconnect clutch isslipping by a threshold amount when the speed/position error isdetected, the driveline disconnect clutch is fully closed to stiffen thedriveline. The driveline disconnect clutch application force or pressuremay be adjusted based on a difference between upstream and downstreamDMF speeds or differences between desired and actual values ofpreviously discussed variables such as driveline frequency amplitude.Method 1900 proceeds to exit after the driveline disconnect clutchapplication force or pressure is adjusted. Method 1900 proceeds to exitafter the driveline disconnect clutch is adjusted.

At 1920, method 1900 judges whether or not driveline conditions arewithin a third operating window. For example, if the upstream anddownstream DMF speed error is greater than a third threshold level. Ifso, method 1900 proceeds to 1922. Otherwise, method 1900 proceeds to1924.

At 1922, method 1900 adjusts torque of the DISG to compensate for thespeed/position or torque differential across the DMF. In one example,torque output of the DISG is increased if the speed on the engine sideof the DMF is greater than the speed on the driveline disconnect clutchside of the DMF. The torque output from the DISG is decreased if thespeed in the on the engine side of the DMF is less than the speed on thedriveline disconnect clutch side of the DMF. In one example, the DMFspeed, position, or torque error is input to a function or table thatoutputs a current demand to adjust DISG torque. Further, the DISG torqueis increased when the sign of the error signal is negative. The DISGtorque is decreased when the sign of the error signal is positive. If anundesirable frequency or magnitude is determined, the torque supplied tothe DISG may be adjusted toward being 180 degrees out of phase of thespeed signal error to dampen the undesired speed oscillations. Method1900 proceeds to exit after the DISG torque is adjusted.

At 1924, method 1900 increases the application rate of the drivelinedisconnect clutch if the driveline disconnect clutch is not closed. Thedriveline disconnect clutch may be closed and the application pressureincreased by increasing a duty cycle of driveline disconnect clutchcontrol signal. Method 1900 proceeds to exit after the drivelinedisconnect clutch is closed.

In other examples, slip of the driveline disconnect clutch, TCC, andDISG torque may be adjusted simultaneously to adjust dampening acrossthe DMF. In this way, method 1900 may adjust one or more actuators toincrease damping or stiffen a driveline when a speed/position,frequency, or torque differential or error across a DMF is greater thana threshold level.

Referring now to FIG. 20, an example sequence for compensating for a DMFin a driveline according to the method of FIG. 19 is shown. The sequenceof FIG. 20 may be provided by the system of FIGS. 1-3.

The first plot from the top of FIG. 20 represents vehicle speed versustime. The Y axis represents vehicle speed and vehicle speed increases inthe direction of the Y axis. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The second plot from the top of FIG. 20 represents driveline disconnectclutch application force versus time. The Y axis represents drivelinedisconnect clutch force and driveline disconnect clutch applicationforce increases in the direction of the Y axis arrow. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The third plot from the top of FIG. 20 represents DMF speed versus time.The Y axis represents DMF speed and DMF speed increases in the directionof the Y axis arrow. The X axis represents time and time increases fromthe left hand side of the figure to the right hand side of the figure.

The fourth plot from the top of FIG. 20 represents TCC application forceversus time. The Y axis represents TCC application force and TCCapplication force increases in the direction of the Y axis arrow. The Xaxis represents time and time increases from the left hand side of thefigure to the right hand side of the figure.

The fifth plot from the top of FIG. 20 represents DISG torque versustime. The Y axis represents DISG torque and DISG torque increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

At time T₃₁, vehicle speed is elevated and the driveline disconnectclutch is fully applied which is indicated by the driveline disconnectclutch application force being at the elevated level. The DMF speed isalso at a higher level and the TCC clutch is closed as indicated by theTCC application force being at the elevated level. The DISG torque isalso at a higher level indicating that the DISG is supplying torque tothe vehicle driveline.

At time T₃₂, vehicle speed reaches zero and the driveline disconnectclutch is opened to allow the engine to stop in response to a lowdriveline torque demand (not shown). The DMF speed is also reduced tozero as engine speed goes to zero. The TCC application force is reducedso that slippage across the torque converter is present. The DISG torqueis also reduced, but the DISG continues to provide torque to thedriveline so that oil pressure may be maintained in the transmission. Inother words, DISG torque is transferred through the torque converterwhile the vehicle and engine are stopped. The DISG torque rotates thetransmission oil pump to maintain transmission oil pressure.

At time T₃₃, the DISG torque increases in response to an increasingdemand torque requested by the driver (not shown). The vehicle speedbegins to increase in response to the increased DISG torque and thedriveline disconnect clutch begins to close in response to theincreasing demand torque. The DMF speed increases as the drivelinedisconnect clutch application force increases to close the drivelinedisconnect clutch. The actual DMF speed begins to oscillate and an errorbetween desired DMF speed and actual DMF speed or between desireddriveline oscillation amplitude and actual driveline oscillationincreases to a level greater than a first threshold. The TCC applicationforce is reduced further to reduce the DMF oscillations and/or speederror.

Between time T₃₃ and time T₃₄, the engine and DISG supply torque to thevehicle driveline. Further, the driveline disconnect clutch remainsfully closed and the DMF speed varies as engine speed varies.

At time T₃₄, vehicle speed reaches zero and the driveline disconnectclutch is opened to allow the engine to stop in response to a lowdriveline torque demand (not shown). The DMF speed is also reduced tozero as engine speed goes to zero. The TCC application force is againreduced so that slippage across the torque converter is present. TheDISG torque is also reduced.

At time T₃₅, the DISG torque increases in response to an increasingdemand torque requested by the driver (not shown). The vehicle speedbegins to increase in response to the increased DISG torque and thedriveline disconnect clutch begins to close in response to theincreasing demand torque. The DMF speed increases as the drivelinedisconnect clutch application force increases to close the drivelinedisconnect clutch. The actual DMF speed begins to oscillate with greateramplitude than at time T₃₃ and an error between desired DMF speed andactual DMF speed or between desired driveline oscillation amplitude andactual driveline oscillation increases to a level greater than a secondthreshold. The driveline disconnect clutch application force is reducedto lower the DMF oscillations and/or speed error.

Between time T₃₅ and time T₃₆, the engine and DISG supply torque to thevehicle driveline. Further, the driveline disconnect clutch remainsfully closed and the DMF speed varies as engine speed varies.

At time T₃₆, vehicle speed reaches zero and the driveline disconnectclutch is opened to allow the engine to stop in response to a lowdriveline torque demand (not shown). The DMF speed is also reduced tozero as engine speed goes to zero. The TCC application force is againreduced so that slippage across the torque converter is present. TheDISG torque is also reduced.

At time T₃₇, the DISG torque increases in response to an increasingdemand torque requested by the driver (not shown). The vehicle speedbegins to increase in response to the increased DISG torque and thedriveline disconnect clutch begins to close in response to theincreasing demand torque. The DMF speed increases as the drivelinedisconnect clutch application force increases to close the drivelinedisconnect clutch. The actual DMF speed begins to oscillate with greateramplitude than at time T₃₅ and an error between desired DMF speed andactual DMF speed or between desired driveline oscillation amplitude andactual driveline oscillation increases to a level greater than a thirdthreshold. The DISG output torque is adjusted (e.g., modulated) todampen the DMF speed, frequency, or torque errors. Additionally, theapplication rate of increasing driveline disconnect clutch applicationforce may be increased to stiffen the driveline.

In this way, different actuators may be adjusted to control drivelinetorque disturbances that may be present at a DMF. The differentactuators may be adjusted according to the disturbance (e.g., speederror, torque error, oscillations) measured at the DMF.

The methods and systems of FIGS. 1-3 and 19-20 provide for adjustingoperation of a hybrid vehicle driveline, comprising: adjusting anactuator in response to a speed or torque differential across a dualmass flywheel (DMF) positioned in the hybrid vehicle driveline betweenan engine and a driveline disconnect clutch where the DMF is drivelinecomponent positioned between the engine and the driveline disconnectclutch. In this way driveline NVH may be reduced.

In one example, the method includes where the actuator is a torqueconverter clutch. The method includes where the actuator is a drivelineintegrated starter/generator. The method includes where the actuator isa driveline disconnect clutch. The method includes where the speeddifferential across the DMF is determined from and engine positionsensor and a positions sensor located in the hybrid vehicle drivelinebetween the DMF and a driveline disconnect clutch. The method includeswhere the driveline disconnect clutch is located in the hybrid vehicledriveline between the DMF and a driveline integrated starter/generator.The method includes where the driveline disconnect clutch selectivelydisengages the engine from a driveline integrated starter/generator anda transmission.

The methods and systems of FIGS. 1-3 and 19-20 also provide foradjusting operation of a hybrid vehicle driveline, comprising: engaginga driveline disconnect clutch to rotate an engine via an electricmachine; and adjusting an actuator in response to a speed or torquedifferential across a dual mass flywheel (DMF) positioned in the hybridvehicle driveline between the engine and a driveline disconnect clutch,where the DMF is a driveline component between the engine and thedriveline disconnect clutch. The method includes where the electricmachine is a driveline integrated starter\generator (DISG) located inthe hybrid vehicle driveline at a location between the drivelinedisconnect clutch and a transmission. The method includes where theactuator is the DISG. The method includes where the DMF transfers enginetorque to an automatic transmission or a dual layshaft—dual clutchtransmission. The method includes where the actuator is a differentactuator for different conditions. The method includes where a frequencycomponent of an engine speed signal is a basis for adjusting theactuator. The method includes where the frequency component isdetermined via a fast Fourier transform (FFT).

The methods and systems of FIGS. 1-3 and 19-20 provide for a hybridvehicle system, comprising: an engine; a dual mass flywheel (DMF)including a first side mechanically coupled to the engine; a drivelinedisconnect clutch mechanically including a first side coupled to asecond side of the dual mass flywheel; a driveline integratedstarter\generator (DISG) including a first side coupled to a second sideof the driveline disconnect clutch; and a controller includingnon-transitory instructions executable to adjust an actuator in responseto a difference across the DMF.

In one example, the hybrid vehicle system further comprises atransmission coupled to a second side of the DISG. The hybrid vehiclesystem includes where the difference is a position difference between afirst side of the DMF and a second side of the DMF as compared to aposition of the first side of the DMF and position of the second side ofthe DMF when no torque is transferred across the DMF. The hybrid vehiclesystem includes where the actuator is the DISG. The hybrid vehiclesystem further comprises additional executable instructions to increaseslip across the driveline disconnect clutch when a difference in speedbetween the first side and the second side of the DMF exceeds athreshold speed. The hybrid vehicle system further comprises additionalexecutable instructions to increase slip across a torque converterclutch when a difference in speed between the first side and the secondside of the DMF exceeds a threshold speed.

The methods and systems of FIGS. 1-3 and 19-20 also provide foradjusting operation of a vehicle driveline, comprising: adjusting anactuator in response engagement of a driveline disconnect clutch todampen oscillation of a dual mass flywheel (DMF) positioned between anengine and the driveline disconnect clutch, and where the DMF is betweenthe engine and the driveline disconnect clutch.

Referring now to FIG. 21, a method is shown for rejecting drivelinetorque disturbances related to application of a driveline disconnectclutch and its transfer function. The method of FIG. 21 may be stored asexecutable instructions in non-transitory memory of controller 12 shownin FIGS. 1-3.

At 2102, method 2100 determines operating conditions. Operatingconditions may include but are not limited to engine speed, DMF inputand output speeds, requested driveline torque, DISG torque, DISG speed,driveline disconnect clutch state, engine speed, torque converterimpeller speed, torque converter turbine speed, and engine torque.Method 2100 proceeds to 2104 after operating conditions are determined.

At 2104, method 2100 judges whether or not a driveline disconnect clutchis open. A driveline disconnect clutch may be determined to be openbased on a variable stored in memory or based on a difference betweenengine speed and DISG speed. If method 2100 judges that the drivelinedisconnect clutch is not open, the answer is no and method 2100 proceedsto exit. If method 2100 judges that the driveline disconnect clutch isopen, the answer is yes and method 2100 proceeds to 2106.

At 2106, method 2100 judges whether or not an engine start is requestedvia the DISG or if engine torque is to be applied to the driveline. Anengine start may be requested when demanded driveline torque is greaterthan a threshold torque. Likewise, a request to provide engine torque tothe driveline may be present when demanded driveline torque is greaterthan a threshold torque. If method 2100 judges that an engine start isrequested via the DISG, or if engine torque is to be applied to thedriveline, the answer is yes and method 2100 proceeds to 2108.Otherwise, the answer is no and method 2100 proceeds to exit.

At 2108, method 2100 judges whether or not a torque sensor is present inthe vehicle driveline at the locations described in FIGS. 1-3. If atorque sensor is judged to be present, the answer is yes and method 2100proceeds to 2110. Otherwise, the answer is no and method 2100 proceedsto 2130.

At 2110, method 2100 determines a difference between a desired drivelineinput torque and actual driveline input torque at a selected locationalong the driveline. In some examples, the selected location for thedriveline input torque may be at a torque converter impeller, a locationbetween a driveline disconnect clutch and a DISG, at a transmissionoutput shaft, at a torque converter turbine, at a launch clutch input,or other driveline location. The actual or measured driveline inputtorque at the selected driveline location is determined from a torquesensor. The desired driveline input torque may be determined from anaccelerator pedal position or other source. The difference in torque isthe desired driveline input torque minus actual driveline input torque.

Alternatively, if the torque sensor is placed in the driveline betweenthe DISG and the driveline disconnect clutch, the torque measured by atorque sensor may be added to a DISG torque command so that the DISGoutputs additional torque to start the engine so that the transmissionis provided a the desired transmission input torque. Method 2100proceeds to 2112.

At 2112, method 2100 adjusts current supplied to the DISG so that thedesired driveline input torque is provided to the driveline at aspecified location even if the driveline disconnect clutch transferfunction is degraded. If the driveline torque sensor is used to feedbackdriveline input torque, the DISG torque is increased when actualdriveline input torque is less than desired driveline input torque. TheDISG torque is decreased when actual driveline input torque is greaterthan desired driveline input torque. In this way, the DISG torque isadjusted in response to a difference between desired driveline inputtorque and actual or measured driveline input torque.

If the driveline torque sensor is implemented as a feed forward sensor,torque sensor output is combined with desired DISG torque to provide thedesired DISG torque at the transmission input or other specifieddriveline location. In this way, a torque sensor may be deployed as afeedback or feed forward device. Method 2100 proceeds to 2114 after DISGtorque is adjusted.

At 2114, method 2100 increases the driveline disconnect clutch pressureto close the driveline disconnect clutch so that the engine may becranked by the DISG or driveline. The driveline disconnect clutchpressure is adjusted by indexing a function that outputs a drivelinedisconnect command or application force based on a desired torque totransfer through the driveline disconnect clutch. Spark and fuel mayalso be supplied at 2114 after the engine is at a predetermined speed orposition. Method 2100 proceeds to 2118 after the driveline disconnectclutch pressure begins to increase.

At 2116, method 2100 judges whether or not the engine has started. Inone example, the engine may be judged to be started when engine speedexceeds a threshold speed. If method 2100 judges that the engine hasstarted, the answer is yes and method 2100 proceeds to 2118. Otherwise,the answer is no and method 2100 returns to 2110.

At 2118, method 2100 judges whether or not engine speed has acceleratedup to and is equal to DISG speed. Engine speed may be judged to be equalto DISG speed when an engine speed sensor and a DISG speed sensor readsubstantially the same speed (e.g., ±20 RPM). If method 2100 judgesengine speed equal to DISG speed, the answer is yes and method 2100proceeds to 2122. Otherwise, the answer is no and method 2100 proceedsto 2120.

At 2120, method 2100 adjusts engine speed to DISG speed. Engine speedmay be adjusted to DISG speed via adjusting engine torque via a throttleand fuel injection. Further, engine speed may be adjusted to reach DISGspeed via fully closing the driveline disconnect clutch. However,completely closing the driveline disconnect clutch before engine speedmatches DISG may increase driveline torque disturbances. Method 2100returns to 2118 after the engine is adjusted to match the DISG speed.

At 2122, method 2100 locks the driveline disconnect clutch. Thedriveline disconnect clutch may be locked by supplying more than athreshold amount of pressure to the driveline disconnect clutch. Method2100 proceeds to exit after the driveline disconnect clutch is locked.

At 2130, method 2100 opens the torque converter clutch (TCC). The torqueconverter clutch is opened so that torque at the torque converterimpeller may be estimated based on torque converter operatingconditions. Alternatively, torque converter turbine torque may beestimated, if desired. Method 2100 proceeds to 2132 after the TCC isopened.

At 2132, method 2100 transitions the DISG into a speed control mode froma torque control mode so that the DISG follows a desired speed. The DISGfollows the desired speed by making torque adjustments to the DISG thatare based on a difference between desired DISG speed and actual DISGspeed. Thus, the DISG speed is controlled via adjusting DISG torque inresponse to actual or measured DISG speed. Additionally, method 2100estimates an amount of torque the driveline disconnect clutch suppliesto start the engine. The desired amount of torque to start the enginemay be empirically determined and stored as a transfer function inmemory. The desired amount of torque to start the engine may betransferred to the engine via the driveline disconnect clutch byindexing a function that describes a driveline disconnect clutchtransfer function. The function outputs a driveline disconnect clutchactuation command that delivers the desired driveline disconnect clutchtorque. The function is indexed via the desired driveline disconnectclutch torque. Method 2100 proceeds to 2134 after the DISG enters speedcontrol mode from torque control mode and determines an amount of torqueto supply the engine via the driveline disconnect clutch so that theengine may be cranked.

At 2134, method 2100 commands the DISG to a desired speed that is afunction of torque converter turbine speed and desired torque converterimpeller torque to achieve a desired torque converter impeller torque.The desired torque converter impeller torque may be determined from anaccelerator input or a controller (e.g., desired driveline torque). Thedesired DISG speed is determined via indexing one or more functions thatdescribe operation of a torque converter (e.g., see FIGS. 45-47). Inparticular, a ratio of torque converter turbine speed to torqueconverter impeller speed is multiplied by a torque converter capacityfactor (e.g., a torque converter transfer function). The result is thenbe multiplied by the torque converter impeller speed squared to providetorque converter impeller torque.

Thus, when the torque converter capacity factor, torque converterimpeller torque, and torque converter turbine speed are known, thetorque converter impeller speed that provides the torque converterimpeller torque may be determined. In this way, the torque convertertransfer function is the basis for providing a desired torque converterimpeller torque when a driveline torque sensor is not provided. The DISGis commanded to the torque converter impeller speed that may provide thedesired torque converter impeller torque even if the drivelinedisconnect clutch application force that provides a desired enginecranking torque is incorrect. Additionally, the amount of torquedetermined to be applied by the driveline disconnect clutch at 2132 maybe added to the DISG torque command that provides the desired DISG speedin speed control mode. In this way, the torque transferred from the DISGto the engine via the driveline disconnect clutch can be added to theDISG torque command so that the DISG achieves the desired torqueconverter impeller speed and torque even as the driveline disconnectclutch is applied. Method 2100 proceeds to 2136 after the DISG speed isadjusted.

At 2136, method 2100 increase the driveline disconnect clutch pressureto close the driveline disconnect clutch so that the engine may becranked by the DISG or driveline. The driveline disconnect clutchpressure is closed to provide the desired amount of torque to crank theengine as determined at 2132. The driveline spark and fuel may also besupplied at 2136 after the engine is at a predetermined speed orposition. Method 2100 proceeds to 2138 after the driveline disconnectclutch pressure begins to increase.

At 2138, method 2100 judges whether or not the engine has started. Inone example, the engine may be judged to be started when engine speedexceeds a threshold speed. If method 2100 judges that the engine hasstarted, the answer is yes and method 2100 proceeds to 2140. Otherwise,the answer is no and method 2100 returns to 2132.

At 2140, method 2100 judges whether or not engine speed has acceleratedup to and is equal to DISG speed. Engine speed may be judged to be equalto DISG speed when an engine speed sensor and a DISG speed sensor readsubstantially the same speed (e.g., ±20 RPM). If method 2100 judgesengine speed equal to DISG speed, the answer is yes and method 2100proceeds to 2144. Otherwise, the answer is no and method 2100 proceedsto 2142.

At 2142, method 2100 adjusts engine speed to DISG speed. Engine speedmay be adjusted to DISG speed via adjusting engine torque via a throttleand fuel injection. Further, engine speed may be adjusted to reach DISGspeed via fully closing the driveline disconnect clutch. However,completely closing the driveline disconnect clutch before engine speedmatches DISG may increase driveline torque disturbances. Method 2100returns to 2140 after the engine is adjusted to match the DISG speed.

At 2144, method 2100 locks the driveline disconnect clutch. Thedriveline disconnect clutch may be locked by supplying more than athreshold amount of pressure to the driveline disconnect clutch. Method2100 proceeds to exit after the driveline disconnect clutch is locked.

In this way, the torque converter transfer function may be a basis forestimating and providing a desired torque converter impeller torque whenno driveline torque sensor is present and if the driveline disconnectclutch torque transfer function is degraded. On the other hand, if adriveline torque sensor is available, the torque sensor output may be abasis for adjusting DISG torque so that a desired torque converterimpeller torque may be provided even if the driveline disconnect clutchtorque transfer function is degraded.

Referring now to FIG. 22, an example sequence for compensating for adriveline disconnect clutch transfer function according to the method ofFIG. 21 is shown. The sequence of FIG. 22 may be provided by the systemof FIGS. 1-3.

The first plot from the top of FIG. 22 represents base DISG torquedemand versus time. In one example, base DISG torque demand is DISGtorque that is provided to the driveline without feedback from adriveline torque sensor or feedback of torque converter operatingconditions. The Y axis represents base DISG torque and base DISG torqueincreases in the direction of the Y axis. The X axis represents time andtime increases from the left hand side of the figure to the right handside of the figure.

The second plot from the top of FIG. 22 represents torque converterimpeller torque versus time. The Y axis represents torque converterimpeller torque and torque converter impeller torque increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure. Solid trace 2202 represents desired torque converterimpeller torque. Dashed trace 2204 represents actual torque converterimpeller torque. Actual torque converter impeller torque equals desiredtorque converter impeller torque when only desired torque converterimpeller torque is visible.

The third plot from the top of FIG. 22 represents driveline disconnectclutch force versus time. The Y axis represents driveline disconnectclutch force and driveline disconnect clutch force increases in thedirection of the Y axis arrow. The driveline disconnect clutch is closedat higher force and is open at lower force. The X axis represents timeand time increases from the left hand side of the figure to the righthand side of the figure.

The fourth plot from the top of FIG. 22 represents a DISG torqueadjustment versus time. An increase in the torque adjustment increasesDISG torque. The Y axis represents DISG adjustment torque and DISGadjustment torque increases in the direction of the Y axis arrow. The Xaxis represents time and time increases from the left hand side of thefigure to the right hand side of the figure.

The fifth plot from the top of FIG. 22 represents engine speed versustime. The Y axis represents engine speed and engine speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

At time T₃₈, DISG torque is at a higher level as is torque converterimpeller torque. The driveline disconnect clutch is closed and there isno DISG torque adjustment since the actual torque converter impellertorque matches the desired torque converter impeller torque. Enginespeed is at an elevated level to indicate that the engine is operating.

At time T₃₉, the base DISG torque is reduced to zero; however, in someexamples the base DISG torque may be greater than zero to providetransmission oil pressure. The engine is stopped and the torqueconverter impeller torque is also reduced to zero. The drivelinedisconnect clutch is opened so that the engine is decoupled from theDISG. Between time T₃₉ and time T₄₀, the engine and DISG remain off.

At time T₄₀, the base DISG torque increases in response to an increasingdriver demand torque (not shown) and in response to the drivelinedisconnect clutch force which may be converted into an amount of torquetransferred through the driveline disconnect clutch to the engine. Theengine is also rotated to be started in response to the driver demandtorque. The engine is rotated by increasing the driveline disconnectclutch application force in response to the driver demand torque so thattorque from the DISG may be transferred to rotate the engine. The DISGtorque transferred to the engine is estimated based on drivelinedisconnect clutch force. In particular, an empirically determinedtransfer function indexed by driveline disconnect clutch force outputs adriveline disconnect clutch torque. The commanded DISG torque is the sumof the driveline disconnect clutch torque and the driver demand torque.In one example, the driver demand torque is a desired torque converterimpeller torque. If the driveline disconnect clutch torque isoverestimated or underestimated, the actual torque converter impellertorque varies from the desired torque converter impeller torque.

In this example, the actual torque converter impeller torque is lessthan the desired torque converter impeller torque as the drivelinedisconnect clutch force is increased. Thus, the driveline disconnectclutch torque has been underestimated and less torque is delivered fromthe DISG to the torque converter impeller. As a result, the DISG torqueis increased to correct the difference between the desired torqueconverter impeller torque and the actual torque converter impellertorque. The DISG torque increase is shown in the DISG torque adjustmentplot which is added to the base DISG torque demand shown in the firstplot and output to the DISG. Further, in some examples, the estimateddriveline disconnect clutch transfer function is adjusted in response tothe DISG torque adjustment. For example, if the DISG torque is increasedby 2 N-m the driveline disconnect clutch transfer function is adjustedto reflect that the driveline disconnect clutch transfers an additional2 N-m at the present driveline disconnect clutch application force.

The actual torque converter impeller torque may be determined via atorque sensor or alternatively from torque converter impeller speed,torque converter turbine speed, and the torque converter capacity factoras described with regard to FIGS. 21 and 45-47. The desired torqueconverter impeller torque may be determined from an accelerator pedalposition or controller demand.

At time T₄₁, the engine is started and the engine has accelerated to thesame speed as the DISG. Further, the driveline disconnect clutch isclosed in response to the engine speed matching the DISG speed. The DISGtorque adjustment is reduced after the driveline disconnect clutch isclosed in response to the actual torque converter impeller torquesubstantially equaling (e.g., ±10 N-m) the desired torque converterimpeller torque.

Thus, the methods and systems of FIGS. 1-3 and 21-22 provide foroperating a hybrid vehicle driveline, comprising: opening a torqueconverter clutch in response to an engine start request; and adjusting adriveline integrated starter/generator (DISG) speed in response to adesired torque converter impeller speed. In this way, compensation for adriveline disconnect clutch may be provided. The method includes whereadjusting the DISG speed includes adjusting the DISG speed as a functionof torque converter turbine speed and desired torque converter impellertorque. The method includes where the desired torque converter impellertorque is based on a driver demand torque. The method includes where theDISG speed is adjusted via adjusting a DISG torque.

In some examples, the method further comprises adjusting the DISG torquein response to an estimated driveline disconnect clutch torque. Themethod includes where the estimated driveline disconnect clutch torqueis based on a driveline disconnect clutch application force. The methodfurther comprises operating the DISG in a speed control mode whenadjusting the DISG speed.

The methods and systems of FIGS. 1-3 and 21-22 provide for operating ahybrid vehicle driveline, comprising: opening a torque converter clutchin response to an engine start request; operating a driveline integratedstarter/generator (DISG) in a speed control mode; adjusting DISG speedin response to a desired torque converter impeller speed; and startingan engine via closing a driveline disconnect clutch. The method includeswhere the driveline disconnect clutch is partially closed in response toa driveline disconnect clutch application force, and where drivelinedisconnect clutch torque is estimated based on a driveline disconnectclutch application force.

In some examples, the method includes where DISG torque is adjusted inresponse to the estimated driveline disconnect clutch torque. The methodfurther comprises adjusting DISG speed in response to a desired torqueconverter impeller torque. The method includes where the DISG speed isadjusted contemporaneously with closing the driveline disconnect clutch.The method further comprises adjusting a driveline disconnect clutchtransfer function in response to a DISG adjustment torque output duringclosing the driveline disconnect clutch. The method includes wherestarting the engine via closing the driveline disconnect clutch includespartially closing the driveline disconnect clutch and then fully closingthe driveline disconnect clutch so that driveline disconnect clutchinput speed matches driveline disconnect output speed when engine speedsubstantially equals DISG speed.

The methods and systems of FIGS. 1-3 and 21-22 provide for a hybridvehicle driveline system, comprising: a torque converter; a drivelineintegrated starter/generator (DISG); an engine; a driveline disconnectclutch positioned in a driveline between the engine and the DISG; and acontroller including executable non-transitory instructions foroperating the DISG in a speed control mode and providing a desiredtorque converter impeller torque via adjusting the DISG speed inresponse to a torque converter turbine speed and the desired torqueconverter impeller torque.

In some examples, the hybrid vehicle driveline system further comprisesadditional executable non-transitory instructions for closing thedriveline disconnect clutch at a first time engine speed substantiallyequals DISG speed after an engine stop. The hybrid vehicle drivelinesystem further comprises additional executable non-transitoryinstructions for closing the driveline disconnect clutch in response toa request to start the engine. The hybrid vehicle driveline systemfurther comprises additional executable non-transitory instructions forestimating driveline disconnect clutch torque based on a drivelinedisconnect clutch application force. The hybrid vehicle driveline systemfurther comprises a DISG speed sensor and a torque converter turbinespeed sensor for determining the torque converter turbine speed. Thehybrid vehicle driveline system includes where the speed control modeincludes adjusting DISG torque to adjust DISG speed.

The methods and systems of FIGS. 1-3 and 21-22 provide for operating ahybrid vehicle driveline, comprising: adjusting torque output of adriveline integrated starter/generator (DISG) in response to adifference between a desired driveline torque and an actual drivelinetorque during at least partially closing a driveline disconnect clutch.In this way, a desired torque may be provided even if estimation ofdriveline disconnect torque includes an error. The method includes wheredesired driveline torque is a desired torque converter impeller torqueand where the actual driveline torque is an actual torque converterimpeller torque.

In one example, the method includes where the desired driveline torqueis based on a driver demand torque. The method further comprisesadjusting torque output of the DISG based on an open-loop estimate ofdriveline disconnect clutch torque. The method includes where theopen-loop estimate of driveline disconnect clutch torque is based on adriveline disconnect clutch application command. The method furthercomprises cranking an engine via closing the driveline disconnectclutch. The method further comprises starting the engine via supplyingfuel and spark to the engine before the driveline disconnect clutch isfully closed.

The methods and systems of FIGS. 1-3 and 21-22 provide for operating ahybrid vehicle driveline, comprising: adjusting torque output of adriveline integrated starter/generator (DISG) in response to adifference between a desired driveline torque and an actual drivelinetorque during at least partially closing a driveline disconnect clutch;and adjusting a driveline disconnect clutch transfer function based onthe difference between the desired driveline torque and the actualdriveline torque. The method includes where the transfer functiondescribes a driveline disconnect clutch torque as a function ofdriveline disconnect clutch application force.

In some examples, the method further comprises cranking an engine via atleast partially closing the driveline disconnect clutch. The methodfurther comprises starting the engine via supplying spark and fuel tothe engine before fully closing the driveline disconnect clutch. Themethod further comprises fully closing the driveline disconnect clutchin response to engine speed substantially equaling DISG speed a firsttime since engine stop. The method includes where the desired drivelinetorque is based on an accelerator pedal input. The method includes wherethe actual driveline torque is based on output of a torque sensor.

The methods and systems of FIGS. 1-3 and 21-22 provide for a hybridvehicle driveline system, comprising: a driveline torque sensor; adriveline integrated starter/generator (DISG); an engine; a drivelinedisconnect clutch positioned in a driveline between the engine and theDISG; and a controller including executable non-transitory instructionsfor adjusting DISG torque output in response to a difference between adesired driveline torque and an output of the driveline torque sensorduring application of the driveline disconnect clutch. The hybridvehicle driveline system further comprises additional executablenon-transitory instructions for closing the driveline disconnect clutchat a first time engine speed substantially equals DISG speed after anengine start.

In some examples, the hybrid vehicle driveline system further comprisesadditional executable non-transitory instructions for closing thedriveline disconnect clutch in response to a request to start theengine. The hybrid vehicle driveline system further comprises additionalexecutable non-transitory instructions for adjusting a drivelinedisconnect clutch transfer function in response to the differencebetween the desired driveline torque and the output of the drivelinetorque sensor. The hybrid vehicle driveline system includes where thedriveline torque sensor is positioned between a torque converterimpeller and the DISG. The hybrid vehicle driveline system includeswhere the driveline torque sensor is positioned between at torqueconverter turbine and a transmission gear set.

Referring now to FIG. 23, a flowchart of a method for improving enginerestart after stopping combustion in an engine is shown. The method ofFIG. 23 may be stored as executable instructions in non-transitorymemory of controller 12 in FIGS. 1-3.

At 2302, method 2300 determines operating conditions. Operatingconditions may include but are not limited to engine speed, engineposition, driveline disconnect clutch state, DISG speed, and ambienttemperature. Method 2300 proceeds to 2304 after operating conditions aredetermined.

At 2304, method 2300 judges whether or not conditions are present toautomatically stop the engine from rotating. In one example, enginerotation may stop when desired driveline torque is less than athreshold. In another example, engine rotation may be stopped whenvehicle speed is less than a threshold speed and when engine torque isless than a threshold torque. If method 2300 judges conditions arepresent to automatically stop engine rotation, method 2300 proceeds to2306. Otherwise, method 2300 proceeds to exit.

At 2306, method 2300 sequentially ceases fuel injection to enginecylinders so that combustion of fuel in engine cylinders is not stoppedmidway during injection of fuel to a particular cylinder. Method 2300proceeds to 2308 after fuel injection is ceased.

At 2308, method 2300 judges whether or not engine speed is below anupper noise vibration and harshness (NVH) threshold speed and above alower NVH threshold speed. If so, the answer is yes and method 2300proceeds to 2310. Otherwise, the answer is no, and method 2300 returnsto 2330.

At 2310, method 2300 judges whether or not the engine crankshaft angleis at a predetermined location as the engine rotates. In one example,the predetermined position is a crankshaft angle within a predeterminednumber of crankshaft degrees after a particular cylinder rotates throughtop-dead-center compression stroke (e.g., within 90 crankshaft degreesafter top-dead-center compression stroke of a cylinder for a fourcylinder engine). If method 2300 judges that the engine crankshaft angleis not at a predetermined location, the answer is no and method 2300returns to 2308. Otherwise, the answer is yes and method 2300 proceedsto 2312.

At 2312, method 2300 commands the starter engage the starter pinionshaft and pinion gear to the engine flywheel ring gear. The starterpinion shaft may be moved via a solenoid, and the starter pinion gearmay begin to rotate when the pinion shaft is fully extended. In otherexamples, the starter pinion shaft and pinion ring gear may beseparately controlled to allow independent activation. Method 2300proceeds to 2314 after the starter pinion shaft and pinion gear arecommanded to be engaged to the engine.

At 2314, method 2300 judges whether or not the pinion shaft and piniongear fully engage the engine flywheel. In one example, the pinion shaftand the pinion gear may be determined to have engaged the engine viasensor outputs (e.g., a limit switch) or via starter current. If method2300 judges that the pinion shaft and pinion gear have engaged theengine, the answer is yes and method 2300 proceeds to 2316. Otherwise,the answer is no and method 2300 proceeds to 2322.

At 2316, method 2300 adjusts the engine throttle to a second positionbased on the pinion shaft and pinion gear engaging the engine flywheelin preparation for a possible operator change of mind to stop theengine. In one example, the second throttle position is more open than afirst throttle position at 2322. The engine throttle position isadjusted to a more open position so as to provide higher engine torqueif an operator change of mind occurs after starter engagement. Enginetorque may be affected when the pinion engages the flywheel. Adjustingthe engine air amount may compensate for the affect an engaged pinionmay have on engine restarting and engine deceleration. Method 2300proceeds to 2318 after the engine throttle position is adjusted.

At 2318, method 2300 judges whether or not an operator change of mindhas occurred since engagement of the starter pinion shaft and starterpinion gear has been commanded. An operator change of mind indicatesthat a driver wishes to continue applying torque to vehicle wheels tomaintain or increase vehicle speed. In one example, an operator changeof mind may be indicted by releasing a brake pedal or increasing anengine torque command via an accelerator pedal. If method 2300 judgesthat an operator change of mind is requested before engine rotationstops, the answer is yes and method 2300 proceeds to 2320. Otherwise,the answer is no and method 2300 returns to 2308.

At 2320, method 2300 cranks the engine via the starter and restarts theengine since the starter pinion shaft and the pinion gear have engagedthe engine flywheel. Fuel and spark are also once again supplied to theengine cylinders to facilitate combustion in engine cylinders. Method2300 exits after the engine is cranked and restarted.

At 2322, method 2300 adjusts the engine throttle to a first positionbased on the pinion shaft and pinion gear not engaging the engineflywheel. In one example, the first throttle position is more closedthan a second throttle position at 2316. The engine throttle position isadjusted to a more closed position so as to reduce engine air flow andreduce oxidation within an exhaust system catalyst. Method 2300 returnsto 2308 after the engine throttle position is adjusted to the firstposition.

At 2330, method 2300 judges whether or not engine speed is lower thanthe lower NVH speed threshold and whether engine speed is above anengagement speed threshold. The engagement speed is an engine speedbelow which the engine may rotate in a reverse direction while theengine is being stopped. If engine speed is above engagement speed andbelow the lower NVH speed threshold, the answer is yes and method 2300proceeds to 2332. Otherwise, the answer is no and method 2300 proceedsto 2350. Method 2300 also ceases to attempt to engage the starter atengine speeds below the engagement speed and above zero engine speed.

At 2332, method 2300 commands the starter pinion shaft and pinion gearto engage the engine flywheel ring gear. The starter pinion shaft andpinion gear may be commanded to engage the engine flywheel ring gear asdescribed at 2312. Method 2300 proceeds to 2334 after the starter pinionshaft and pinion gear are commanded to engage the engine flywheel.

At 2334, method 2300 judges whether or not the pinion shaft and thepinion gear engage the engine flywheel ring gear. Method 2300 judges ifthe pinion shaft and pinion gear engage the flywheel ring gear asdescribed at 2314. If method 2300 judges that the flywheel is engaged bythe pinion gear and pinion shaft, the answer is yes and method 2300proceeds to 2336. Otherwise, the answer is no and method 2300 proceedsto 2342.

At 2336, method 2300 adjusts the throttle position to a fourth position.Since engaging the starter pinion shaft and pinion gear to the engineflywheel occurs at a lower engine speed, it may be desirable to adjustengine braking via controlling the engine air amount via the throttle toa different amount as compared to when engagement of the starter pinionshaft and pinion gear to the engine flywheel ring gear is attempted at ahigher engine speed. Further, adjusting the engine air amount maycompensate for engaging the pinion. In one example, the fourth positionis a position where the throttle is more closed than the first andsecond positions at 2322 and 2316. Further, the fourth throttle positionis more open than the third throttle position at 2342 to prepare for anoperator change of mind condition. Adjusting the throttle based onengine speed may also provide finer control of engine position at enginestop. Method 2300 proceeds to 2338 after the throttle is adjusted to thefourth position.

At 2338, method 2300 judges whether or not an operator change of mind ispresent. An operator change of mind may be determined as described at2318. If method 2300 judges that an operator change of mind is present,the answer is yes and method 2300 proceeds to 2340. Otherwise, theanswer is no and method 2300 returns to 2310.

At 2340, method 2300 cranks the engine for starting and supplies sparkand fuel to the engine. Method 2300 may crank the engine via the starteror the DISG as described at 2320. Method 2300 proceeds to exit after theengine is cranked and restarted in response to the operator change ofmind.

At 2342, method 2300 adjusts the throttle to a third position. The thirdposition may be a throttle position that is closed open than the fourthposition described at 2336. The third position may also be a throttleposition that is more closed than the first and second positionsdescribed at 2322 and 2316. Method 2300 returns to 2310 after the enginethrottle position is adjusted.

At 2350, method 2300 commands the starter pinion shaft and pinion gearto engage the engine flywheel ring gear after the engine has stoppedrotating if it is not engaged. Engaging the starter pinion shaft andpinion gear after engine stop may reduce starter and/or ring gear wear.Further, by engaging the starter pinion shaft and pinion gear before theengine is restarted it may be possible to reduce engine starting time.Method 2300 proceeds to 2352 after the starter pinion shaft and piniongear have been commanded to engage the engine flywheel ring gear.

At 2352, the engine is restarted automatically in response to operatingconditions after the engine ceases to rotate. The engine may berestarted in response to an engine torque request by an operator or inresponse to an operator releasing a brake. An automatic engine startoccurs when the engine is restarted without an operator actuating oroperating a device that has a sole function of starting an engine (e.g.,a start key switch). An automatic engine start may be initiated by anoperator actuating or operating a device that has more than one functionsuch as a brake pedal which can apply vehicle brakes or secondarily asan indication when to start the engine. Method 2300 restarts the enginevia a starter motor or via the DISG and proceeds to exit.

In this way, the method of FIG. 23 may adjust a position of a throttlein response to starter engagement to further improve engine restartingin case of an operator change of mind. Further, the method of FIG. 23adjusts the throttle position during engine stopping according to enginespeed so as to improve the engine stopping position by limiting enginereverse rotation.

Referring now to FIG. 24, an example sequence for improving enginerestarting and engine after stopping combustion according to the methodof FIG. 23 is shown. The sequence of FIG. 24 may be provided by thesystem of FIGS. 1-3.

The first plot from the top of FIG. 24 represents engine speed versustime. The Y axis represents engine speed and engine speed increases inthe direction of the Y axis. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure. Horizontal line 2402 represents an upper NVH engine speedthreshold. Horizontal line 2404 represents a lower NVH engine speedthreshold. Horizontal line 2406 represents a pinion engagement speedthreshold where the pinion is not engaged if engine speed is belowhorizontal line 2406 unless the engine has stopped rotating. Theengagement threshold may reduce starter degradation.

The second plot from the top of FIG. 24 represents fuel injection stateversus time. The Y axis represents fuel injection state. Fuel injectionis active when the trace is at a higher level. Fuel injection is stoppedwhen the trace is at a lower level. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The third plot from the top of FIG. 24 represents engine throttleposition versus time. The Y axis represents engine throttle position andengine throttle position increases in the direction of the Y axis arrow.The X axis represents time and time increases from the left hand side ofthe figure to the right hand side of the figure.

The fourth plot from the top of FIG. 24 represents starter pinion stateversus time. The Y axis represents starter pinion state and levels ofengagement are described next to the Y axis. The pinion is returned whenthe trace is at the level of RET. The pinion is advanced but not engagedwhen the trace is at the level ADV. The pinion is engage with the engineflywheel when the trace is at the level ENG. The X axis represents timeand time increases from the left hand side of the figure to the righthand side of the figure.

The fifth plot from the top of FIG. 24 represents vehicle brake state(e.g., friction brake state) versus time. The Y axis represents vehiclebrake state and the brake is applied when the trace is at a higherlevel. The brake is released when the trace is at a lower level. The Xaxis represents time and time increases from the left hand side of thefigure to the right hand side of the figure.

At time T₄₂, engine speed is elevated, fuel injection is active, thethrottle is partially open, the starter is not engaged, and the brake isnot applied. These conditions are indicative of a vehicle that iscruising at a moderate speed (e.g. 40 MPH). Between time T₄₂ and timeT₄₃, the vehicle brakes are applied to slow the vehicle. In theillustrated conditions, the vehicle may be moving or may have stoppedbetween time T₄₂ and time T₄₃.

At time T₄₃, engine combustion is stopped in response to applying thevehicle brake and a reduction in throttle position which is based ondriver demand torque. As a result, engine speed is reduced to being ator less than the upper NVH engine speed threshold 2402. The starterpinion is commanded to engage the engine flywheel, but the pinion onlyadvances and does not fully engage the engine flywheel. The throttleposition is reduced in response to engine speed being less than theupper NVH threshold and being greater than the lower NVH threshold.Further, the throttle position is adjusted in response to the starterpinion position being advanced but not engaged. The throttle is openedto a first position 2410. The engine speed continues to decrease and thepinion engages the flywheel just before time T₄₄. The engine throttleposition is adjusted to a second position 2412 in response to the pinionengaging the engine flywheel. The second throttle position is more openthan the first position. By opening the throttle more after the pinionis engaged, it may be possible to prepare for an operator change of mindso that engine restarting may be improved.

At time T₄₄, the brake pedal is release by the operator which isinterpreted as an operator change of mind to stop the engine. The fuelinjection is reactivated and the starter provides the engine startingtorque via the engaged pinion. The engine restarts and the pinion isreturned shortly thereafter. Between time T₄₄ and time T₄₅, the engineis accelerated and decelerated over varying driving conditions. Thebrake is applied again just before time T₄₅.

At time T₄₅, combustion is stopped in the engine and the engine beginsto decelerate. Shortly thereafter, engine speed is reduced to less thanthe upper NVH engine speed threshold 2402. The pinion is advanced inresponse to engine speed being less than the NVH upper engine speedthreshold and being greater than the lower NVH engine speed threshold,but the pinion does not fully engage the engine flywheel. The enginethrottle is adjusted to a first position 2410 in response to the enginespeed and pinion state. The engine speed continues to decrease and thethrottle is adjusted to a third position 2414 when engine speed is lessthan lower NVH engine speed threshold 2404 and greater than engagementthreshold 2406. The third position 2414 is less open than the firstposition 2410 and second position 2412. The pinion engages the engineflywheel while engine speed is less than lower NVH engine speedthreshold 2404 and greater than engagement threshold 2406. Consequently,the throttle is adjusted to a fourth position in response to pinionposition and engine speed. The fourth position 2416 is more open thanthe third position 2414. The fourth position may provide additional airto the engine so that the engine may be restarted easier in case of anoperator change of mind. The engine speed reaches zero without anoperator change of mind and the pinion remains engaged.

At time T₄₆, the operator releases the brake and the engine is restartedvia the engaged pinion in response to the brake being released. Fuelinjection is also reactivated in response to releasing the brake and asubsequent request to start the engine.

In this way, a position of an engine throttle may be adjusted to improveengine restarting while an engine is being stopped. Adjusting enginethrottle position in response to engine speed and pinion state duringengine stopping may help to provide the engine with an amount of airthat may improve engine starting. Additionally, if the pinion does notengage before engine stopping, the adjusted throttle position mayimprove engine stopping by controlling engine air amount predictablyduring engine stopping.

The methods and systems of FIGS. 1-3 and 23-24 provide for stoppingrotation of an engine, comprising: ceasing fuel delivery to enginecylinders combusting air and fuel; commanding engagement of a starterfrom a state not engaged with the engine to engaged with the engine; andadjusting a position of a throttle based on whether or not the starterengages the engine. In this way, the engine may be more prepared tostart if an operator has a change of mind. The method includes where thestarter engages the engine via a pinion gear. The method includes wherethe throttle is adjusted to a first position when the starter does notengage the engine within a first engine speed range. The method includeswhere the throttle is adjusted to a second position when the starterengages the engine within the first engine speed range, the secondposition more open than the first position.

In some examples, the method further comprises where the starter iscommanded to engage the engine within a predetermined crankshaft angularwindow. The method includes where the crankshaft angular window iswithin ±40 crankshaft degrees of top-dead-center of a cylinder stroke.The method includes where the engine speed is decreasing duringcommanding engagement of the starter.

The methods and systems of FIGS. 1-3 and 23-24 provide for stoppingrotation of an engine, comprising: ceasing fuel delivery to enginecylinders combusting air and fuel; commanding engagement of a starterthat is not engaged to the engine to engage the engine; and adjusting aposition of a throttle based on whether or not the starter engages theengine and engine speed. The method includes where the throttle positionis adjusted to a more closed position at engine speeds less than athreshold speed and to a more open position at engine speeds greaterthan the threshold speed. The method includes where the throttle isadjusted to a first position when the starter does not engage the enginewithin a first engine speed range. The method includes where thethrottle is adjusted to a second position when the starter engages theengine within the first engine speed range, the second position moreopen than the first position. The method includes where the throttle isadjusted to a third position when the starter does not engage the enginewithin a second engine speed range. The method includes where thethrottle is adjusted to a fourth position when the starter engages theengine within the second engine speed range, the fourth position moreopen than the third position.

The methods and systems of FIGS. 1-3 and 23-24 provide for a vehiclesystem, comprising: an engine including a throttle; a dual mass flywheel(DMF) including a first side mechanically coupled to the engine; adriveline disconnect clutch mechanically including a first side coupledto a second side of the dual mass flywheel; a starter including a basestate where the starter is not engaged to the engine; a transmissionselectively coupled to the engine via the driveline disconnect clutch;and a controller including non-transitory instructions executable toadjust a position of the throttle during an engine stop based on whetheror not the starter engages the engine in response to an engine stoprequest and before an engine stop.

In some examples, the vehicle system includes where the throttle isadjusted to a first position in response to the starter does not engagethe engine. The vehicle system includes where the throttle is adjustedto a second position in response to the starter engaging the engine, thesecond position more open than the first position. The vehicle systemfurther comprises additional instructions to adjust the throttleposition in response to an engine speed. The vehicle system furthercomprises additional instructions to engage the starter at apredetermined crankshaft location. The vehicle system includes where thepredetermined crankshaft location is ±40 crankshaft degrees fromtop-dead-center of a cylinder compression stroke. The vehicle systemfurther comprises additional instructions to stop attempting to engagethe starter at engine speeds below an engagement speed and above zeroengine speed.

Referring now to FIG. 25, a flowchart of a method for adjusting engineshutdown speed profile and engine rotation stop position is shown. Themethod of FIG. 25 may be stored as executable instructions innon-transitory memory of controller 12 in FIGS. 1-3.

At 2502, method 2500 judges whether or not an engine stop rotationrequest has occurred. An engine stop rotation request may be provided bya controller or an operator. The controller may automatically stop theengine without the operator supplying input from a dedicated actuatorthat has a sole function of stopping and/or starting the engine. Forexample, an automatic engine stop does not occur when an operator setsan ignition switch to an off state. Alternatively, an automatic enginestop may occur when an operator releases an accelerator pedal. If method2500 judges that an engine stop is requested, the answer is yes andmethod 2500 proceeds to 2504. Otherwise, the answer is no and method2500 proceeds to exit.

At 2504, method 2500 judges whether or not engine rotation is to bestopped with the driveline disconnect clutch slipping. Method 2500judges whether or not the engine should be stopped while the drivelinedisconnect clutch is slipping based on operating conditions. In oneexample, the engine may be stopped without a slipping drivelinedisconnect clutch when it is desirable to stop the engine in a shortperiod of time. For example, it may be desirable to stop the enginequickly when engine speed is relatively low at the time of the enginestop request. On the other hand, the engine may be stopped while thedriveline disconnect clutch is slipping when engine speed is relativelyhigh at the time of the engine stop request. It should also be mentionedthat engine rotation can be stopped with an open driveline disconnectclutch during some conditions. If method 2500 judges that enginerotation is to be stopped with the driveline disconnect clutch slipping,the answer is yes and method 2500 proceeds to 2530. Otherwise, theanswer is no and method 2500 proceeds to 2506.

At 2530, method 2500 determines desired transmission clutch oil linepressure. In one example, the desired transmission clutch oil linepressure may be based on an amount of clutch pressure that will hold avehicle stopped on a road while the engine has stopped rotating. Thus,the desired transmission clutch oil line pressure may increase if thevehicle is stopped on a hill. In one example, the desired transmissionclutch oil line pressure is empirically determined and stored in a tableor function that is indexed by road grade and vehicle mass. The tableoutputs the desired transmission clutch oil line pressure in response toroad grade and vehicle mass. Method 2500 proceeds to 2532 after thedesired transmission clutch oil line pressure is determined.

At 2532, method 2500 rotates the DISG at a speed that provides thedesired transmission clutch oil line pressure by rotating thetransmission oil pump. The DISG is coupled to a torque converterimpeller, and the torque converter impeller is fluidly coupled to thetorque converter turbine. The transmission oil pump is driven by thetorque converter impeller, and the transmission oil pump supplies oilpressure to transmission clutches when rotated. In one example, thedesired transmission oil line pressure indexes a table that includesempirically determined values of DISG speed that provide the desiredtransmission clutch oil line pressure. The DISG speed is output from thetable and the DISG is speed is controlled to the value output from thetable. Method 2500 proceeds to 2534 after the DISG begins rotating atthe desired speed.

At 2534, method 2500 stops fuel flow and spark to engine cylinders. Fuelflow to cylinders may be stopped by closing fuel injectors. Further,fuel flow may be stopped in a sequential order based on enginecombustion order so that cylinders are not partially fueled when enginerotation is commanded to stop. Method 2500 proceeds to 2536 after fuelflow and spark to engine cylinders stops.

At 2536, method 2500 slips the driveline disconnect clutch to achieve adesired engine speed trajectory. In one example, an empiricallydetermined driveline disconnect clutch apply or slip trajectories arestored in a memory and are applied to the driveline disconnect clutchwhen stop of engine is requested. The slip trajectory table appliespressure to the driveline disconnect clutch at different rates dependingon the engine speed when the engine stop request is made. Alternatively,an empirically determined transfer function that outputs a drivelinedisconnect clutch application force or pressure based on a desireddriveline disconnect clutch pressure that is the basis for operating thedriveline disconnect clutch. Additionally, the slip trajectory mayinclude timing of when the pressure is to be supplied to the drivelinedisconnect clutch. For example, the pressure may be applied to thedriveline disconnect clutch a specified number of crankshaft degreesafter a last amount of fuel is delivered to an engine cylinder beforeengine stop. Thus, the initial time of driveline disconnect clutchpressure application and the rate at which pressure is applied to thedriveline disconnect clutch is stored in memory and applied when anengine stop request is issued. Method 2500 proceeds to 2538 afterapplication of the driveline disconnect clutch pressure profile isinitiated.

At 2538, method 2500 commands transmission clutches to tie thetransmission output shaft to the transmission case. The transmissionoutput shaft may be tied to the transmission by simultaneously applyingto transmission clutches other than the driveline disconnect clutch atthe same time as described in U.S. patent application Ser. No.12/833,788. Method 2500 proceeds to 2540 after the transmission iscommanded to a tied state.

At 2540, method 2500 opens the driveline disconnect clutch. Thedriveline disconnect clutch may be opened when engine speed is atsubstantially zero (e.g., 100 RPM or less) and the engine has stopped ata desired position. Alternatively, the driveline disconnect clutch maybe opened when engine speed falls to a predetermined value. Thus, byvarying operation of the driveline disconnect clutch, method 2500 cancontrol the engine speed trajectory partially or completely down to zeroengine speed. Method 2500 proceeds to exit after the drivelinedisconnect clutch is opened.

At 2506, method 2500 closes the driveline disconnect clutch if thedriveline disconnect clutch is not already closed. The drivelinedisconnect clutch may be closed by increasing a duty cycle signal thatincreases the driveline disconnect clutch apply pressure. Method 2500proceeds to 2508 after the driveline disconnect clutch is closed.

At 2508, method 2500 stops fuel flow and spark to engine cylinders. Fuelflow and spark may be stopped as is described at 2534. Method 2500proceeds to 2510 after fuel and spark delivery to engine cylinders isstopped.

At 2510, method 2500 adjusts DISG speed and torque to provide a desiredengine speed profile during stopping of engine rotation. In one example,an empirically determined group of engine speed trajectories are storedin a memory and are used as a basis to stop the engine. For example, ifengine speed is greater than that of the engine speed trajectoryretrieved from memory, DISG torque absorbing is increased to direct theengine speed to the desired engine speed profile. If engine speed isless than that of the engine speed trajectory retrieved from memory,DISG torque is increased to direct the engine speed to the desiredengine speed profile. The engine speed trajectory table slows the enginespeed at different rates depending on the engine speed when the enginestop request is made. Additionally, the engine speed trajectory mayinclude timing of when the engine speed trajectory is to be controlledvia the DISG. For example, the engine speed trajectory may be controlledby the DISG for a specified number of crankshaft degrees after a lastamount of fuel is delivered to an engine cylinder before engine stop.Thus, the initial application time of engine speed profile and the rateat of engine speed reduction is stored in memory and controlled by theDISG when an engine stop request is issued. Method 2500 proceeds to 2512after application of the driveline disconnect clutch pressure profile isinitiated.

At 2512, method 2500 commands transmission clutches to tie thetransmission output shaft to the transmission case. The transmissionoutput shaft may be tied to the transmission by simultaneously applyingto transmission clutches other than the driveline disconnect clutch atthe same time as described in U.S. patent application Ser. No.12/833,788 which is hereby fully incorporated by reference. Method 2500proceeds to 2514 after the transmission is commanded to a tied state.

At 2514, method 2500 opens the driveline disconnect clutch at apredetermined engine speed. The driveline disconnect clutch is opened sothat the engine can coast to zero speed while the DISG continues torotate and supply pressure to transmission clutches while the engine isstopped. In one example, the driveline disconnect clutch is opened atpredetermined engine speed that is based on the engine speed where theengine stop was initiated (e.g., the engine speed where fuel flow toengine cylinders stopped) and the rate of engine speed decay. Further,the driveline disconnect clutch may be opened at a particular crankshaftangle to further control engine stopping position. A table or functionindexed by rate of engine speed decay and engine speed where engine stopwas requested outputs the engine position where the driveline disconnectclutch is opened. In one example, the position corresponds to an engineposition that improves the possibility of stopping at the desired engineposition (e.g., during a predetermined crankshaft interval of a cylinderin a compression stroke). Method 2500 proceeds to 2516 after thedriveline disconnect clutch is opened.

At 2516, method 2500 determines a desired transmission clutch linepressure. The desired transmission clutch line pressure is determined asis described at 2530. Method 2500 proceeds to 2518 after the desiredtransmission clutch oil line pressure is determined.

At 2518, method 2500 rotates the DISG to maintain the desiredtransmission clutch oil line pressure. The DISG may be rotated as isdescribed at 2532. Method 2500 proceeds to exit after the DISG iscommanded to supply the desired transmission clutch oil line pressure.It should be noted that the DISG may be periodically stopped andrestarted to maintain transmission clutch oil line pressure. If thetransmission clutch oil line pressure has a slow leak rate, the DISG maybe commanded off. The DISG may be reactivated if the transmission clutchoil line pressure declines to a threshold level.

In this way, engine stopping position may be controlled for a hybridvehicle. The driveline disconnect clutch may adjust an engine stoppingprofile from idle speed to zero speed via periodically providing torquefrom the DISG to the engine so that the engine stops at a desiredposition.

Referring now to FIG. 26, an example sequence for stopping an engineaccording to the method of FIG. 25 is shown. The sequence of FIG. 26 maybe provided by the system of FIGS. 1-3.

The first plot from the top of FIG. 26 represents engine speed versustime. The Y axis represents engine speed and engine speed increases inthe direction of the Y axis. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The second plot from the top of FIG. 26 represents DISG speed versustime. The Y axis represents DISG speed and DISG speed increases in thedirection of the Y axis. The X axis represents time and time increasesfrom the left hand side of the figure to the right hand side of thefigure.

The third plot from the top of FIG. 26 represents driveline disconnectclutch application force (e.g., force applied to close the drivelinedisconnect clutch) versus time. The Y axis represents drivelinedisconnect clutch application force and driveline disconnect clutchapplication force increase in the direction of the Y axis. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The fourth plot from the top of FIG. 26 represents fuel delivery stateversus time. The Y axis represents fuel delivery state and fuel isdelivered to the engine when the trace is at a higher level. Fuel is notdelivered to the engine when the trace is at a lower level. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The fifth plot from the top of FIG. 26 represents transmission tie-upstate versus time. The Y axis represents transmission tie-up state andthe transmission is tied-up when the trace is at a higher level. Thetransmission is not tied-up when the trace is at a lower level. The Xaxis represents time and time increases from the left hand side of thefigure to the right hand side of the figure.

At time T₄₇, engine speed and DISG speed are equal and at an elevatedlevel. The engine is mechanically coupled to the DISG via the drivelinedisconnect clutch. The driveline disconnect clutch is fully closed whendriveline disconnect clutch input speed is equal to driveline disconnectclutch output speed. Further, the driveline disconnect clutch is fullyclosed when the driveline disconnect force is at a higher level. Fuel isbeing delivered to the engine as indicated by the fuel delivery statebeing at higher level. The transmission is not tied-up since thetransmission tie-up state is at a lower level.

At time T₄₈, the engine is commanded to an off state in response tooperating conditions (e.g., a low engine torque demand and an appliedvehicle brake). Fuel delivery to the engine is stopped as indicated bythe fuel delivery state transitioning to a lower level. Additionally,the DISG speed/torque are adjusted to control the engine speed andposition trajectory in response to the request to stop the engine. Inone example, an engine speed/position trajectory is stored in memory andDISG torque is adjusted in response to a difference between actualengine speed and the desired engine speed trajectory that is stored inmemory. For example, if the actual engine speed is less than the desiredengine speed at a particular time after the engine stop request, DISGtorque is increased to move actual engine speed to the desired enginespeed. In another example, if a particular engine position (e.g.,cylinder number one top-dead-center compression stroke) is ahead ofwhere it is desired at a particular time after requesting engine stop,DISG negative torque may be increased to slow the engine at a greaterrate.

At time T₄₉, the driveline disconnect clutch is opened in response tothe engine reaching a predetermined speed. Further, clutches of thetransmission begin to be applied so that the transmission output shaftis tied to the transmission case and the vehicle chassis. By opening thedriveline disconnect clutch at a predetermined speed, it may be possibleto better control engine speed during engine stopping while allowing theDISG to operate. In this example, the DISG is stopped but in otherexamples it may continue to rotate so as to provide motive force tooperate the transmission oil pump. The engine and DISG are stoppedshortly after the disconnect clutch is opened.

In this way, an engine may be stopped such that engine position may becontrolled during stopping. By controlling the engine stop position, itmay be possible to improve the engine restart performance consistency.

At time T₅₀, the DISG is accelerated and provides torque to the vehicledriveline in response to an operator releasing a brake pedal (notshown). Further, the DISG helps to start the engine. In particular, thedriveline disconnect clutch is partially closed to transfer torque fromthe DISG to the engine. Fuel and spark are provided to the engine tosupport combustion in the engine as indicated by the fuel delivery statetransitioning to a higher level. Finally, the transmission clutches arealso opened so as to untie the transmission in response to releasing thebrake. The driveline disconnect clutch is fully closed when the enginespeed reaches the DISG speed.

In this way, the engine may be restarted while torque is being providedto the vehicle driveline to accelerate the vehicle. Further, thedriveline disconnect clutch is operated in a way that may reducedriveline torque disturbances.

Between time T₅₀ and time T₅₁, the engine and DISG supply torque to thevehicle driveline based on operator demand. In this example, thedriveline disconnect clutch remains closed; however, it may also openwithout stopping the engine on occasion.

At time T₅₁, the engine is commanded to an off state in response tooperating conditions (e.g., a low engine torque demand and an appliedvehicle brake). Fuel delivery to the engine is stopped as indicated bythe fuel delivery state transitioning to a lower level. The drivelinedisconnect clutch is also commanded to slip via reducing the drivelinedisconnect clutch application force. In one example, the drivelinedisconnect clutch slip rate is stored in memory as a function of timesince engine stop request. The slip rate may be increased or decreasedif the engine speed varies from a desired engine speed. For example, ifengine speed is less than a desired engine speed at a particular timeafter the engine stop request, driveline disconnect clutch slip may bereduced by increasing the driveling disconnect clutch application force.In this way, additional torque may be provided by the DISG to the engineso that engine speed matched desired engine speed. The DISG speed iscommanded to a speed that allows the transmission oil pump to provide adesired oil pressure.

At time T₅₂, engine speed reaches a predetermined speed and transmissionclutches are applied to tie the transmission output shaft to the vehiclechassis. The DISG continues to rotate so that oil pressure is providedto transmission clutches.

In this way, a driveline disconnect clutch may slip during an enginestopping procedure to provide a desired engine stopping position. Insome examples, the desired engine stopping position is where aparticular cylinder piston stops within a predetermined number ofdegrees before top-dead-center compression stroke of the cylinder.

The methods and systems of FIGS. 1-3 and 25-26 provide for an enginestopping method, comprising: adjusting a speed of a driveline integratedstarter/generator (DISG) to a desired speed that provides a desiredtransmission clutch oil line pressure in response to a request to stopengine rotation; and slipping a driveline disconnect clutch in adriveline between the DISG and the engine to stop the engine at adesired position. The method includes where the desired position apredetermined number of crankshaft degrees before top-dead-centercompression stroke of a selected cylinder. The method further comprisesceasing fuel flow and spark to engine cylinders in response to therequest to stop engine rotation. The method further comprises tying atransmission output shaft to a transmission case in response to therequest to stop engine rotation.

In some examples, the method further comprises opening the drivelinedisconnect clutch at substantially zero engine speed. The method alsofurther comprises continuing to rotate the DISG while the engine is atzero speed. The method further comprises activating and deactivating theDISG while the engine speed is zero.

The methods and systems of FIGS. 1-3 and 25-26 also provide for anengine stopping method, comprising: closing a driveline disconnectclutch in response to a request to stop engine rotation; adjusting aspeed of a driveline integrated starter/generator (DISG) to a desiredengine speed profile that decelerates toward zero engine speed; andopening the driveline disconnect clutch at a predetermined engine speed.The method further comprises tying a transmission output shaft to atransmission case in response to the request to stop the engine. Themethod further comprises ceasing fuel flow and spark to engine cylindersin response to the request to stop the engine. The method includes wherethe driveline disconnect clutch is in a driveline positioned between anengine and the DISG.

In some examples, the method further comprises opening the drivelinedisconnect clutch at a predetermined position. The method includes wherespeed of the DISG is increased when engine speed is less than thedesired engine speed profile. The method includes where speed of theDISG is decreased when engine speed is greater than the desired enginespeed profile.

The methods and systems of FIGS. 1-3 and 25-26 provide for a vehiclesystem, comprising: an engine; a dual mass flywheel (DMF) including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller including executableinstructions stored in non-transitory memory to adjust operation of thedriveline disconnect clutch in response to a request to stop enginerotation.

In some examples, the vehicle system includes where the drivelinedisconnect clutch is at least partially closed. The vehicle systemincludes where the driveline disconnect clutch is fully closed. Thevehicle system further comprises additional instructions to open thedriveline disconnect clutch at a predetermined engine speed. The vehiclesystem further comprises operating the DISG at a speed that provides adesired transmission clutch oil line pressure. The vehicle systemfurther comprises additional instructions to selectively deactivate theDISG at zero engine speed.

Referring now to FIG. 27, a method for stopping an engine when a vehiclein which the engine operates is parked on varying grades is shown. Themethod of FIG. 27 may be stored as executable instructions innon-transitory memory of controller 12 in FIGS. 1-3.

At 2702, method 2700 judges whether or not a vehicle in which an engineis operated is stopped. In one example, the vehicle may be determined tobe stopped when vehicle speed is zero. If method 2700 judges that thevehicle is stopped the answer is yes and method 2700 proceeds to 2704.Otherwise, the answer is no and method 2700 proceeds to exit.

At 2704, method 2700 judges whether or not engine stopping conditionsare met. In one example, engine stopping conditions may include but arenot limited to driver demand torque being less than a threshold torque,engine speed being less than a threshold speed, and vehicle brakeapplied. In other examples, other engine stopping conditions may beapplied. If engine stopping conditions are present the answer is yes andmethod 2700 proceeds to 2706. Otherwise, the answer is no and method2700 proceeds to exit.

At 2706, method 2700 estimates road grade and vehicle mass. In oneexample road grade may be determined via an inclinometer. Vehicle massmay be determined as described at 904 of FIG. 9. Additionally, method2700 stops engine rotation. Method 2700 proceeds to 2708 after vehiclemass and road grade are determined.

At 2708, method 2700 judges whether or not road grade is greater than afirst threshold road grade. In one example, the first threshold andother threshold road grades may be a function of vehicle mass. Forexample, if the vehicle mass increases the first threshold road grademay decrease. If method 2700 judges that the present road grade isgreater than a first threshold road grade, the answer is yes and method2700 proceeds to 2716. Otherwise, the answer is no and method 2700proceeds to 2710.

At 2710, method 2700 maintains transmission oil pressure to allowtransmission gear shifting and shifts from a lower gear (e.g., firstgear) to a higher gear (e.g., second gear) if the transmission is notalready in second gear. By shifting to a higher gear, the vehicle massis effectively increased at the vehicle wheels so that it is moredifficult to move the vehicle. The transmission oil pressure may bemaintained via an electric oil pump. Method 2700 proceeds to 2712 afterthe transmission is shifted.

At 2712, method 2700 judges whether or not vehicle acceleration or anincreased torque demand is requested. In one example, increased driverdemand is determined from accelerator pedal position. If method 2700judges that vehicle acceleration or increased torque demand isrequested, the answer is yes and method 2700 proceeds to 2714.Otherwise, method 2700 returns to 2710.

At 2714, method 2700 increases torque delivered to the driveline anddownshifts the transmission to a lower gear (e.g., first gear) toaccelerate the vehicle. Driveline torque may be increased via the DISGor via the engine after starting the engine. The engine may be startedvia cranking by the DISG or a starter with lower power output capacity.Method 2700 proceeds to exit after the transmission is shifted to firstgear and torque to the driveline is increased.

At 2716, method 2700 judges whether or not road grade is greater than asecond threshold road grade. If method 2700 judges that the present roadgrade is greater than a second threshold road grade, the answer is yesand method 2700 proceeds to 2724. Otherwise, the answer is no and method2700 proceeds to 2718.

At 2718, method 2700 maintains transmission oil pressure to allowtransmission gear shifting and shifts to a higher gear than second gear(e.g., 3^(rd) gear) if the transmission is not already in a higher gear.By shifting to a higher gear than second gear, the vehicle mass iseffectively increased at the vehicle wheels so that it is more difficultto move the vehicle. The transmission oil pressure may be maintained viaan electric oil pump. Method 2700 proceeds to 2718 after thetransmission is downshifted.

At 2720, method 2700 judges whether or not vehicle acceleration or anincreased torque demand is requested. In one example, increased driverdemand is determined from accelerator pedal position. If method 2700judges that vehicle acceleration or increased torque demand isrequested, the answer is yes and method 2700 proceeds to 2722.Otherwise, method 2700 returns to 2718.

At 2722, method 2700 increases torque delivered to the driveline anddownshifts the transmission to first gear to accelerate the vehicle.Driveline torque may be increased via the DISG or via the engine afterstarting the engine. The engine may be started via cranking by the DISGor a starter with lower power output capacity. Method 2700 proceeds toexit after the transmission is shifted to first gear and as the amountof torque delivered to the driveline is increased.

At 2724, method 2700 applies vehicle brakes, maintains transmission oilpressure to allow transmission gear shifting, and shifts to first if itis not already in first gear. By shifting to first gear and applying thebrakes the vehicle may be ready to accelerate while being stopped on agrade. Further, by not applying brakes on lower grades, brake wear maybe reduced while reducing vehicle movement. The transmission oilpressure may be maintained via an electric oil pump. Method 2700proceeds to 2726 after the vehicle brakes are applied.

At 2726, method 2700 judges whether or not vehicle acceleration or anincreased torque demand is requested. If method 2700 judges that vehicleacceleration or increased torque demand is requested, the answer is yesand method 2700 proceeds to 2728. Otherwise, method 2700 returns to2724.

At 2728, method 2700 increases torque delivered to the driveline andreleases vehicle brakes so that the vehicle may accelerate. Drivelinetorque may be increased via the DISG or via the engine after startingthe engine. The engine may be started via cranking by the DISG or astarter with lower power output capacity. Method 2700 proceeds to exitafter the vehicle brakes are released.

As described herein, engine shutdown or stop operation, such as whencoming to or at a vehicle stop, may be used to conserve fuel. Duringsuch operation, the driveline disconnect clutch may be opened. Thereforewhen the vehicle is at rest, possibly on an uphill grade, the engine isoften shutdown to rest. Thus, an alternative pressure source, other thanthe engine, may be used to maintain the transmission hydraulic pressurewhile the engine is off. In some examples, an electric auxiliary pumpmay be used to maintain the transmission hydraulic pressure. In otherexamples, the DISG speed does not drop to zero when the vehicle isstopped, but is held at low speed, typically well below idle (e.g.,200-500 RPM) to maintain the transmission hydraulic pressure. Underthese conditions, the torque converter output torque is either zero (asthe input speed is zero), or is a value that may not be sufficient toprevent the vehicle from rolling backwards when the brake is released.One approach applies the wheel brakes to prevent the vehicle fromrolling backwards; however, while effective in some cases this can alsolead to degraded vehicle launch performance, or require a grade sensor.

Another issue may be that when the operator depresses the brake pedal,one or both of vehicle brakes and regenerative braking may be applied,based on operating conditions. For example, the braking torque generatedby the DISG during regenerative braking (with or without the engineshutdown and the driveline disconnect clutch opened) may be balancedwith the friction wheel brake torque to provide desired rate ofdeceleration that corresponds to the brake pedal pressure. Since whenthe vehicle comes to a stop the regenerative brake torque diminishes toperform a hill hold function, a greater portion of the friction braketorque has to be “reserved” thus reducing the benefit of regenerativebraking. Thus, alternative hill holding approaches may be desirable inorder to increase the ability to utilize regenerative braking.

In one example, the torque converter based automatic transmission may beequipped with a one-way clutch. In this way, if the transmission fluidpressure is maintained while the vehicle is stationary and if thetransmission is held in gear (as opposed to neutral, for example), thenthe one way clutch acts as a mechanical hill holding device to preventthe vehicle from rolling backwards when the vehicle is on an uphillgrade. However, depending upon the vehicle mass and the grade angle,holding the transmission in a lower gear, e.g. first gear, may only slowthe vehicle roll back when the brake is released on a steeper grade,e.g. 6%. In this example, if the transmission is in first gear, thetorque which is a function of the sine of the grade angle and thevehicle mass may be sufficient to overcome the one-way clutch holdingtorque. Thus, in one example, the transmission may be held in a gearthat is higher than first gear if this is required to prevent thevehicle from rolling backwards on the maximum design grade. For example,the transmission may be shifted to a higher gear before coming to a stopso as to enable hill holding, such as based on an estimated grade duringvehicle travel.

Above a pre-determined grade, e.g. 6%, the longitudinal sensor basedgrade detection system may be used to determine grade. Thus, in someexamples, the controller may determine if the current grade is in excessof an upper limit, and if so, the brake system may be applied inaddition to assist in hill holding operation to prevent vehicle rollback.

For heavier vehicles or vehicle that may have higher loads, such as apick-up truck, it may be advantageous to apply multiple clutches in thetransmission to increase the maximum transmission holding torque. Byapplying two or more clutches while the vehicle is stationary, thetransmission input can be “tied” to the transmission housing. Thisapproach can also be used as part of an engine restart vehicle launchtechnique to shape the transmission output torque as the vehicle pullsaway from a stop. Therefore by maintaining the transmission hydraulicpressure while the vehicle is stopped and applying the clutch(s) toeither hold a gear or to put the transmission in a tie-up state, thevehicle can be prevented from rolling backwards when the operatorreleases the brake.

Referring now to FIG. 28, an example sequence for stopping an enginewhen a vehicle in which the engine operates is parked on a gradeaccording to the method of FIG. 27 is shown. The sequence of FIG. 28 maybe provided by the system of FIGS. 1-3.

The first plot from the top of FIG. 28 represents vehicle speed versustime. The Y axis represents vehicle speed and vehicle speed increases inthe direction of the Y axis. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The second plot from the top of FIG. 28 represents road grade versustime. The Y axis represents road grade and road grade increases in thedirection of the Y axis. The X axis represents time and time increasesfrom the left hand side of the figure to the right hand side of thefigure. Horizontal line 2802 represents a first threshold grade.Horizontal line 2804 represents a second threshold grade that is greaterthan the first threshold grade.

The third plot from the top of FIG. 28 represents transmission gearversus time. The Y axis represents transmission gear and the respectivetransmission gears are identified along the Y axis. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The fourth plot from the top of FIG. 28 represents engine state versustime. The Y axis represents engine state and the engine is operatingwhen the engine state trace is at a higher level. The engine is stoppedwhen the engine state trace is at a lower level. The X axis representstime and time increases from the left hand side of the figure to theright hand side of the figure.

The fifth plot from the top of FIG. 28 represents vehicle brake state(e.g., friction brake state) versus time. The Y axis represents vehiclebrake state and the vehicle brake is applied when the brake state traceis at a higher level. The brake is not applied when the brake state isat a lower level. The X axis represents time and time increases from theleft hand side of the figure to the right hand side of the figure.

The sixth plot from the top of FIG. 28 represents vehicle brake pedalstate versus time. The Y axis represents vehicle brake pedal state andthe vehicle brake pedal is applied when the brake pedal state trace isat a higher level. The brake pedal is not applied when the brake pedalstate is at a lower level. The X axis represents time and time increasesfrom the left hand side of the figure to the right hand side of thefigure.

At time T₅₃, vehicle speed is elevated, road grade is near zero, and thetransmission is in 5^(th) gear indicating that the vehicle is cruisingat speed. The engine is operating and the brake pedal and brakes are notapplied.

Between time T₅₃ and time T₅₄, the vehicle decelerates and downshiftsfrom 5^(th) gear to 1^(st) gear in response to a lower driver demandtorque (not shown). The vehicle brake is applied as is the brake pedal.Shortly before time T₅₄, the transmission is shifted to 2^(nd) gear inresponse to the road grade and an engine stop request after the vehicleis stopped.

At time T₅₄, the engine is stopped and the transmission is held in2^(nd) gear to increase the vehicle's effective mass as presented to thevehicle's wheels. The vehicle brake pedal and brakes remain applied;however, in some examples after the vehicle is stopped, the vehiclebrake may be released when the brake pedal is applied after thetransmission is shifted to a higher gear. The road grade remains nearzero and below the first grade threshold 2802.

At time T₅₅, the brake pedal is released by a driver. The vehicle brakesare released in response to releasing the brake pedal. The transmissionis also downshifted into first gear to improve vehicle acceleration inresponse to the driver releasing the brake. The engine is also startedin response to the driver releasing the brake. The vehicle begins toaccelerate a short time after the brake pedal is release in response toan increasing driver demand torque.

Between time T₅₅ and time T₅₆, the vehicle accelerates and thendecelerates in response to a driver demand torque and application of thebrake pedal and brakes as indicated by the brake state and the brakepedal state. The transmission also shifts from 1^(st) through 5^(th)gear while the vehicle is accelerating and decelerating. The road gradealso increases and is greater than first threshold road grade 2802 bytime T₅₆. The brake pedal and brakes are applied by the driver todecelerate the vehicle.

At time T₅₆, the vehicle stops and the transmission is downshifted to1^(st) gear as indicated by the vehicle speed and transmission traces.The engine continues to operate when the vehicle stops.

At time T₅₇, the transmission is upshifted to 3^(rd) gear in response tovehicle grade being greater than the first threshold grade 2802 and arequest to stop the engine. Shifting the transmission increases thevehicle's effective mass at the vehicle wheels so that it is moredifficult to roll down the increased grade. The engine is stoppedshortly after the transmission is upshifted. The brake pedal and vehiclebrakes remain applied by the driver; however, in some examples after thevehicle is stopped, the vehicle brake may be released when the brakepedal is applied after the transmission is shifted to a higher gear.

At time T₅₈, the driver releases the brake pedal and the brakes arereleased in response to the brake pedal being released. The transmissionis downshifted from 3^(rd) gear to 1^(st) gear and the engine is startedas indicated by the transition in engine state. The brakes and enginechange state in response to the brake pedal being released. The vehiclebegins to accelerate shortly after the brake pedal is released inresponse to an increasing driver demand torque (not shown).

Between time T₅₈ and time T₅₉, the vehicle accelerates and thendecelerates in response to a driver demand torque and to application ofthe brake pedal and brakes as indicated by the brake state and the brakepedal state. The transmission also shifts from 1^(st) through 5^(th)gear while the vehicle is accelerating and decelerating. The road gradealso increases and is greater than second threshold road grade 2804 bytime T₅₉. The brake pedal and brakes are applied by the driver todecelerate the vehicle. The vehicle comes to a stop before time T₅₉.

At time T₅₉, the engine is stopped and the vehicle brakes are applied inresponse to the brake pedal, a low driver demand torque, and the roadgrade being greater than threshold road grade 2804. The brake pedaltrace and the brake state trace are at higher levels to indicate thatboth the brakes and the brake pedal are applied.

At time T₆₀, the driver releases the brake pedal and the engine isstarted in response to the released brake pedal. The brake state remainsat a higher level to indicate that the brakes are applied. The brakesremain applied in response to the road grade being greater than thesecond road grade threshold 2804 and driver demand torque being lessthan a threshold torque (not shown). The vehicle is stationary asindicated by the vehicle speed trace being zero.

At time T₆₁, the driver demand torque increases (not shown) and thevehicle brake is released in response to the increased driver demandtorque. The vehicle also begins to accelerate in response to theincreased driver demand torque as indicated by the vehicle speedincreasing.

In this way, the vehicle and drivetrain may respond to changing vehiclegrade so that a vehicle remains substantially stationary when the engineis stopped while the vehicle is on a grade. As the vehicle is stopped onincreasing grades, vehicle movement reducing measures are progressivelyincreased.

The methods and systems of FIGS. 1-3 and 27-28 provide for a vehiclestopping method, comprising: upshifting a transmission to a gear inresponse to a road grade when a vehicle is stationary; and automaticallystopping an engine of the vehicle in response to vehicle conditions. Themethod includes where the gear number increases as the road gradeincreases. The method includes where automatically stopping the engineincludes stopping the engine in response to a low driver demand torque.The method includes where automatically stopping the engine furtherincludes stopping the engine in response to vehicle speed. The methodincludes where automatically stopping the engine includes stopping theengine in response to a vehicle brake pedal state. The method includeswhere the transmission is shifted without a driver shift request, andwhere the transmission is an automatic transmission. The method furthercomprises downshifting the transmission in response to an increasingdriver demand torque after upshifting the transmission.

The methods and systems of FIGS. 1-3 and 27-28 also provide for avehicle stopping method, comprising: during a first condition,upshifting a transmission to a first gear ratio in response to a firstroad grade when a vehicle is stationary; during a second condition,upshifting the transmission to a second gear ratio in response to asecond road grade when the vehicle is stationary; and automaticallystopping an engine in response to vehicle conditions. The methodincludes where the first gear ratio is a lower gear ratio than thesecond gear ratio, and where the transmission is not in first gear whenthe transmission is shifted to the first gear ratio. The method furthercomprises downshifting the transmission in response to an increasingdriver demand torque after upshifting the transmission during the firstand second conditions.

In some examples, the method includes where the second road grade isgreater than the first road grade. The method further comprisesmaintaining transmission oil pressure while shifting the transmission.The method includes where the engine is stopped before the transmissionis shifted, and where the transmission oil pressure is maintained via adriveline integrated starter/generator. The method further comprisesselecting the first gear ratio and the second gear ratio in response tovehicle mass.

The methods and systems of FIGS. 1-3 and 27-28 provide for a vehiclesystem, comprising: an engine; a transmission in selective mechanicalcommunication with the engine; and a controller including executableinstructions stored in non-transitory memory for shifting thetransmission to a gear in response to road grade while a vehicle inwhich the engine operates is stationary, the controller also includinginstructions to apply vehicle brakes in response to road grade. Thevehicle system includes where the engine is stopped before thetransmission is shifted, and where the transmission oil pressure ismaintained via a driveline integrated starter/generator. The vehiclesystem further comprises additional instructions for selecting the firstgear ratio and the second gear ratio in response to vehicle mass.

In some examples, the vehicle system further comprises additionalinstructions for downshifting the transmission in response to anincreasing driver demand torque after the vehicle is stationary. Thevehicle system further comprises additional instructions for releasingthe vehicle brakes in response to an increasing driver demand torqueafter the vehicle is stationary. The vehicle system includes where thetransmission is an automatic transmission.

Referring now to FIGS. 29A and 29B, a flowchart of a method forproviding vehicle braking via the vehicle driveline is shown. The methodof FIGS. 29A and 29B may be stored as executable instructionsnon-transitory memory in the system of FIGS. 1-3.

At 2902, method 2900 determined operating conditions. Operatingconditions may include but are not limited to vehicle speed, enginespeed, brake pedal position, desired driveline torque, DISG speed, andbattery state of charge. Method 2900 proceeds to 2904 after operatingconditions are determined.

At 2904, method 2900 judges whether or not conditions are present toautomatically stop the engine. The engine may be automatically stoppedin response to vehicle conditions and not in response to an input thathas a sole function of starting and/or stopping engine rotation (e.g.,an off/on key switch). For example, when an operator turns an enginestop key to the engine, the engine is not automatically stopped.However, if the operator releases an accelerator pedal, which has afunction of supplying a driveline torque demand, the engine may beautomatically stopped in response to a low torque demand. If method 2900judges that conditions are present to automatically stop the engine, theanswer is yes and method 2900 proceeds to 2906. Otherwise, the answer isno and method 2900 proceeds to exit.

At 2906, method 2900 judges whether or not driveline vehicle braking isrequested. Driveline vehicle braking may be requested during vehicledeceleration to reduce the amount of wheel braking used to deceleratethe vehicle. For example, driveline braking via an engine or DISG may beprovided when a vehicle is descending a hill so that a smaller amount ofwheel braking may be used to decelerate the vehicle. In one example,method 2900 may judge that driveline braking is requested when thevehicle is accelerating and a low driveline torque request is present.If method 2900 judges that driveline braking is requested, the answer isyes and method 2900 proceeds to 2910. Otherwise, the answer is no andmethod 2900 proceeds to 2908.

At 2908, method 2900 supplies a desired torque to the driveline via theDISG and/or the engine. Positive engine torque may be supplied by theengine combusting an air-fuel mixture and rotating the driveline. TheDISG may provide torque in response to an amount of current flowing tothe DISG. Method 2900 proceeds to exit after the desired torque issupplied to the driveline.

At 2910, method 2900 judges whether or not the DISG has a capacity toprovide the desired amount of vehicle braking without the engine. In oneexample, method 2900 judges whether or not the DISG has the capacity forproviding the desired amount of vehicle braking without the enginebraking in response to vehicle speed, selected transmission gear, andDISG torque absorbing capacity. In particular, a table describingempirically determined torque absorbing capacity of the DISG is indexedby DISG speed, as determined from vehicle speed and selected gear. Ifmethod 2900 judges that the DISG has the capacity for providing thedesired amount of driveline braking without the engine providingbraking, the answer is yes and method 2900 proceeds to 2916. Otherwise,the answer is no and method 2900 proceeds to 2912.

At 2912, method 2900 rotates the engine without providing fuel to theengine and engine rotational losses are increased so that drivelinebraking may be increased. The engine rotational losses may be increasedby adjusting valve timing. In one example, intake valves are opened neartop-dead-center intake stroke and exhaust valves are opened early in theexpansion stroke (e.g., before 90 crankshaft degrees aftertop-dead-center compression stroke) to increase engine rotational lossesand increase driveline braking. The engine is rotated by closing thedriveline disconnect clutch which couples the engine to the remainingportion of the driveline as shown in FIGS. 1-3. Method 2900 proceeds to2914 after the engine is rotated and engine rotating losses areincreased.

At 2914, method 2900 converts vehicle kinetic energy into electricalenergy. In particular, the DISG is put in a generator mode whererotational energy from vehicle wheels is converted into electricalenergy and stored to a battery or other energy storage device. In oneexample, the rotational energy provided by the driveline from thevehicle wheels, through the transmission, through the torque converter,and to the DISG is converted to electrical energy generating currentflow through a stator. The electrical energy may then be stored in anenergy storage device. Method 2900 returns to 2906 after vehicle kineticenergy begins to be converted to electrical energy.

At 2916, method 2900 judges whether or not energy storage device SOC isgreater than a threshold charge amount. In one example, SOC may beestimated based on a voltage across the energy storage device. If method2900 judges that the energy storage device SOC is greater than athreshold amount, the answer is yes and method 2900 proceeds to 2930.Otherwise, the answer is no and method 2900 proceeds to 2918.

Additionally, at 2916 method 2900 can proceed to 2930 when a driverrequests increased driveline braking. For example, if a driver presses abutton to enter a hill decent mode, method 2900 proceeds to 2930 toincrease driveline braking.

At 2918, method 2900 transitions the DISG to a speed control mode fromtorque control mode. In speed control mode, DISG torque output isadjusted in response to DISG speed so that DISG speed converges to adesired DISG speed. In one example, DISG torque is increased when DISGspeed is less than actual DISG speed. Likewise, DISG torque is decreasedwhen DISG speed is greater than actual DISG speed. The DISG is operatedin a speed control mode so that the DISG can react to the drivelinespeed variations caused by the torque changes. As a result, the torqueconverter impeller may rotate at a desired constant speed duringdriveline disconnect clutch transitions so that torque transferredthrough the torque converter is more constant. In this way, the DISGreduces driveline torque disturbances that may be caused by thedriveline disconnect clutch opening. Method 2900 proceeds to 2920 afterthe DISG is put into speed control mode.

At 2920, method 2900 stops engine rotation by opening or disengaging thedriveline disconnect clutch and stopping fuel flow to engine cylinders.The driveline disconnect clutch may be opened before fuel flow to enginecylinders is stopped so that the non-combusting engine does not reducedriveline speed and torque at the torque converter impeller. Method 2900proceeds to 2922 after engine rotation is stopped and the drivelinedisconnect clutch begins to open.

At 2922, method 2900 adjusts the torque capacity of torque converterclutch (TCC) to reject driveline disconnect clutch opening disturbances.When the driveline mode is changed to energy regeneration mode and thedriveline disconnect clutch starts to open and instantaneous impellerspeed may vary because the amount of torque transferred from the engineto the driveline is changed. In one example, the torque capacity of theTCC is modulated and controlled to obtain smooth transitions betweenchanges in state of the driveline disconnect clutch. As such, a moreconsistent vehicle speed may be maintained when the driveline disconnectclutch is opened. For example, if the torque converter impeller speedbegins to decrease when the disconnect clutch opens, the TCC may beadjusted slip an increased amount. Method 2900 proceeds to 2924 afterthe TCC is adjusted.

At 2924, method 2900 converts vehicle kinetic energy into electricalenergy as described at 2914. The electrical energy is directed to anelectrical energy conversion storage device where it is held and may beused at a later time. The electrical energy conversion device may be abattery or a capacitor. Method 2900 proceeds to 2926 after conversion ofvehicle kinetic energy to electrical energy begins.

At 2926, method 2900 transitions to a torque control mode after anydisturbance from opening the driveline disconnect clutch has beenmitigated. Method 2900 also adjusts the DISG to provide negative torquein an amount that is equal to what the engine provides duringdeceleration fuel shut off.

An amount of braking torque that an engine may provide may beempirically determined and stored in memory. The engine braking amountmay include adjustments for valve timing, engine oil temperature, enginespeed, throttle position, and barometric pressure. The adjustments maybe added to a base engine braking torque that is characterized atnominal valve timings, engine temperature, engine speed, throttleposition, and barometric pressure. For example, engine braking torquemay be determined at an engine oil temperature of 90° C., engine speedof 1500 RPM, base valve timing, closed throttle, and barometric pressureof 100 kPA. Engine braking torque may be adjusted from the base brakingtorque as operating conditions deviate from the base conditions.

Present engine operating conditions (e.g., oil temperature, valvetiming, etc.) are determined and are the basis for indexing empiricallydetermined tables and/or functions that output engine braking torque atthe present operating conditions. Once the engine braking torque atpresent operating conditions is determined, DISG torque is adjusted tothe engine braking torque. By adjusting the DISG torque to the enginebraking torque, it may be possible to transition from providing brakingtorque using the DISG to providing braking torque via the engine withoutthe DISG providing braking torque when energy conversion device SOC isgreater than a threshold.

The engine conditions may be continuously monitored so that negative orregeneration DISG torque may be revised as engine operating conditionschange. For example, if engine oil temperature decreases and enginefriction increases, negative DISG torque that emulates engine brakingtorque when fuel flow is stopped to the engine may be increased toreflect the change in engine braking torque. Method 2900 proceeds to2928 after negative DISG torque is adjusted to engine braking torquewhen the engine is rotated without fuel being supplied to the engine andwhen there is no combustion in the engine.

At 2928, method 2900 automatically activates and increases selectedvehicle electrical loads to extent the amount of time the DISG maycontinue to provide driveline braking. For example, if the vehicletravels down a hill for an extended duration, the energy storage devicemay become fully charged so that it may not accept additional charge.During such conditions, the DISG may stop providing charge to the energystorage device to reduce the possibility of energy storage devicedegradation. However, it may be possible for the DISG to continue toprovide charge to the energy storage device if additional charge isprovided to vehicle systems so that the energy storage device chargedoes not increase.

In one example, current supplied to selected electrically operatedvehicle systems is increased when energy storage device state of chargeis greater than a threshold level. In other examples, current suppliedto selected electrically operated vehicle systems is increased whencharge provided by the DISG to the battery is greater than a thresholdrate of charge. In some examples, when energy storage device state ofcharge is greater than a threshold level, the engine is rotated, theDISG ceases to operate in generation mode, and current supplied to theselected electrically operated vehicle systems continues until charge ofthe energy storage device is reduced to a second threshold level andthen the DISG returns to generating mode. The engine stops rotating whencharge of the energy storage device is less than a threshold level.

Selected electrically operated vehicle systems that may be automaticallyactivated and turned on or supplied more current than requested. Theselected electrically operated vehicle systems may include but are notlimited to front and rear windshield defrosting devices, exhaust aftertreatment heating devices, electric pumps, and lights. For example, thefront and rear windshield defrosters may be activated without notifyingthe driver so that the driver may be unaware electrical energy is beingconsumed to lengthen DISG operation in regeneration mode. Further,output of an electric pump (e.g., a fuel pump) may be increased byincreasing pump current without the driver noticing. Likewise, emissionsystem heaters and vehicle lights may be activated to extend DISGoperation in regeneration mode. Method 2900 returns to 2906 afterelectrical loads are adjusted.

At 2930, method 2900 increases slip across a torque converter clutch(TCC) if the TCC is locked. If the TCC is slipping, slip across the TCCis further increased. Slipping the TCC reduces torque disturbances thatmay be introduced to the driveline via connecting and disconnecting thedriveline disconnect clutch. In one example, the TCC is placed in acontrolled slip mode at 2934 and the TCC is modulated in response totorque converter impeller speed changes. Method 2900 proceeds to 2932after slip across the TCC is adjusted.

At 2932, method 2900 puts the DISG in speed control mode after exitingtorque control mode and adjusts DISG torque to maintain DISG speed at asubstantially constant value (e.g., ±50 RPM of a commanded DISG speed).In one example, DISG speed is compared against a desired DISG speed, andcurrent supplied to the DISG is adjusted in response to a difference inDISG speed and desired DISG speed. If DISG speed is less than thedesired DISG speed, additional current is supplied to the DISG toincrease DISG torque and speed. If DISG speed is greater than thedesired DISG speed, current supplied to the DISG is decreased todecrease DISG speed and torque supplied to the driveline. Putting theDISG in speed control mode allows the DISG to control driveline torquewithout causing driveline speed changes which may be undesirable to adriver. Method 2900 proceeds to 2934 after the DISG is put in speedcontrol mode.

At 2934, method 2900 sets the TCC capacity at a constant value ortransitions to a new control gain value for TCC closed loop slipcontrol. For example, a signal controlling the amount of torque the TCCtransfers across the torque converter is adjusted as torque converterimpeller speed changes to reduce driveline disturbances. In one example,the TCC slip amount is adjusted according to a TCC transfer functionthat outputs a TCC control signal duty cycle. The TCC transfer functionis indexed based on torque converter impeller speed and torque converterturbine speed. Method 2900 proceeds to 2936 after the TCC capacity isadjusted.

At 2936, method 2900 judges whether or not a starter other than the DISGis present. In some examples, if a starter other than the DISG is notavailable or in a degraded state, method 2900 may judge the non-DISGstarter as not being present. If method 2900 judges that a starter otherthan the DISG is not present, the answer is no and method 2900 proceedsto 2950. Otherwise, the answer is yes and method 2900 proceeds to 2938.

At 2950, method 2900 at least partially closes the driveline disconnectclutch while the DISG is in speed control mode to rotate the engine. Inone example, the driveline disconnect clutch is closed to a positionthat provides a desire engine cranking speed (e.g., 250 RPM). Thedesired cranking speed may vary depending on operating conditions andmay be as high as the DISG speed in some examples. Closing the drivelinedisconnect clutch causes driveline torque to be transferred to theengine. Thus, current supplied to the DISG may be increased when thedriveline disconnect clutch is engaged so as to maintain DISG speed. Inthis way, torque transferred across the torque converter may bemaintained at a constant level since the torque converter impeller speedis constant. Method 2900 proceeds to 2952 after the driveline disconnectclutch is at least partially closed.

At 2952, method 2900 provides spark and fuel to engine cylinders tostart the engine. In one example, fuel is provided to engine cylindersvia direct fuel injectors. Method 2900 proceeds to 2954 after spark andfuel are supplied to engine cylinders.

At 2954, method 2900 judges whether or not combustion is occurring inengine cylinders. In one example, method 2900 judges that combustion ispresent in engine cylinders when engine torque output increases. Anincrease in engine speed may be indicative of combustion in enginecylinders. In other examples, combustion in engine cylinders may bedetermined via cylinder pressure sensors. If method 2900 determinescombustion is present in engine cylinders, the answer is yes and method2900 proceeds to 2956. Otherwise, the answer is no and method 2900returns to 2954.

At 2956, method 2900 opens the driveline disconnect clutch and adjustsDISG torque. Opening the driveline disconnect clutch can reduce theamount of torque transferred from the DISG and driveline to start theengine when the driveline disconnect clutch is disengaged before theengine begins to produce more torque to accelerate the engine to theDISG speed. Opening the driveline disconnect clutch also reduces theamount of torque provided by the driveline to accelerate the engine.Therefore, the DISG torque may be reduced to keep the DISG at a constantspeed when the driveline disconnect clutch is released. In exampleswhere vehicle kinetic energy is rotating the DISG, the amount of torqueabsorbed by the DISG may be adjusted. Method 2900 proceeds to 2940 afterthe driveline disconnect clutch is opened.

At 2938, method 2900 rotates the engine via a starter other than theDISG. In one example, the starter has a lower power output capacity thanthe DISG and the starter selectively engages a flywheel coupled to anengine crankshaft. The starter provides an engine cranking speed of lessthan 250 RPM. Spark and fuel are also supplied to the engine at 2938.Method 2900 proceeds to 2940 after the engine begins to rotate.

At 2940, method 2900 accelerates the engine speed to a speed synchronouswith the DISG. The engine is accelerated by adjusting fuel, spark, andthe cylinder air amount to engine cylinders. Method 2900 proceeds to2942 after engine speed reaches DISG speed.

At 2942, method 2900 holds the engine speed at DISG speed and providessubstantially zero net torque (e.g., ±10 N-m) out of the enginecrankshaft. In other words, the engine torque is adjusted just highenough to overcome engine losses and rotate the engine at the DISGspeed. Method 2900 proceeds to 2944 after engine net torque issubstantially zero.

At 2944, method 2900 closes the driveline disconnect clutch.Substantially no torque is transferred between the driveline and theengine when the driveline disconnect clutch is closed so that a smoothtransition between not operating the engine and operating the engine isprovided. The engine is operated at substantially DISG speed (e.g., ±25RPM) when the driveline disconnect clutch is closed. Method 2900proceeds to 2946 after the driveline disconnect clutch is closed.

At 2946, method 2900 ramps down engine combustion torque (e.g., enginetorque provided by combustion) and then fuel injection is stopped sothat the engine is not rotating under its own power. Engine outputtorque is ramped down by reducing cylinder air amounts and cylinder fuelamounts. Further, engine rotational losses are increased via adjustingengine valve timing. For example, intake valves of a cylinder may beopened near top-dead-center intake stroke and exhaust valves of thecylinder may be opened between top-dead-center compression stroke and 45crankshaft degrees after top-dead-center compression stroke to increaseengine rotational losses. Valves of other engine cylinders may beoperated in a similar manner. Negative torque generated by the DISGduring regeneration may be decreased to smooth the transition from theengine providing combustion torque and the engine providing brakingtorque during fuel shut off. Further, the negative DISG torque may beadjusted to maintain a constant torque converter impeller speed whilethe DISG is converting kinetic energy into electrical energy. In thisway, the rotating engine may increase a load applied to the driveline toprovide a desired amount of driveline braking to the vehicle. Method2900 proceeds to 2948 after engine combustion torque is ramped down.

In one example, the amount of regenerative torque requested by the DISGshould be consistent with the amount of engine braking torque that ispresently available as described at 2926. The engine braking torque canbe estimated based on the engine oil temperature, engine friction andpumping at the current impeller speed. Once the system converts toengine braking, the actual engine braking can be compared to theestimated engine braking and a correction can be made to the estimate.In this way, the vehicle may decelerate at the same rate for both enginebraking and regenerative braking when the brake pedal is not beingpressed.

At 2948, method 2900 holds DISG torque substantially constant andreturns the TCC to closed loop slip control. For example, the TCCcommand signal may be adjusted to provide a desired speed differentialbetween the torque converter impeller and the torque converter turbine.Method 2900 returns to 2906 after the TCC is returned to a closed loopslip control mode.

In an alternative example, engine rotation may commence and fuel andspark may be withheld from the engine while the engine rotates up to theDISG speed. The driveline disconnect clutch initially closes a smallamount and a higher level of slip is present across the drivelinedisconnect clutch. The DISG may be transitioned from a generator stateto a motor state to reduce any driveline torque disturbance asaccelerating the engine provides additional negative torque to thedriveline. Additional pressure is applied to the driveline disconnectclutch to increase the negative torque provided by the engine to thedriveline. DISG torque is adjusted while the DISG is in speed controlmode to provide the desired level of driveline braking. In one example,DISG current is adjusted to provide a desired vehicle deceleration rate.

In another example, 2936-2956 may be replaced with a step where theengine remains at zero rotation while vehicle braking via frictionbrakes (e.g., wheel brakes) is increased without driver input while DISGtorque absorption (e.g., converting rotational mechanical energy intoelectrical energy) is decreased. The friction braking force may beincreased proportional to the reduction in DISG driveline braking. Thus,vehicle brakes are automatically applied while the driveline brakingprovided by the DISG is reduced.

In this way, the method of FIGS. 29A-B provides driveline braking sothat fuel may be conserved by converting kinetic energy into electricalenergy. Further, the method may reduce driveline torque disturbances viacontrolling the DISG, TCC, and other driveline components.

Referring now to FIG. 30, an example sequence for providing vehiclebraking via a driveline according to the method of FIGS. 29A-B is shown.The sequence of FIG. 30 may be provided by the system of FIGS. 1-3.

The first plot from the top of FIG. 30 represents torque converterturbine speed versus time. The Y axis represents torque converterturbine speed and torque converter turbine speed increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The second plot from the top of FIG. 30 represents engine speed versustime. The Y axis represents engine speed and engine speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The third plot from the top of FIG. 30 represents torque converterclutch (TCC) application force versus time. The Y axis represents TCCapplication force and TCC application force increases in the directionof the Y axis arrow. The X axis represents time and time increases fromthe left hand side of the figure to the right hand side of the figure.

The fourth plot from the top of FIG. 30 represents driveline disconnectclutch torque versus time. The Y axis represents driveline disconnectclutch torque and driveline disconnect clutch torque increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The fifth plot from the top of FIG. 30 represents DISG output torqueversus time. The Y axis represents DISG output torque and DISG outputtorque increases in the direction of the Y axis arrow. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The sixth plot from the top of FIG. 30 represents engine torque versustime. The Y axis represents engine torque and engine torque increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

At time T₆₂, the engine is stopped, the turbine speed is elevated, andthe DISG is providing a negative (e.g., braking torque) to thedriveline. The TCC clutch is locked and the driveline disconnect clutchis open and not transmitting torque.

At time T₆₃, the torque converter clutch slip is increased in responseto a request to restart the engine. The request to restart the engine isbased on an increase in driver demand torque (not shown). The TCC forcedecreases as the torque converter clutch slip is increased. The enginespeed remains constant, the driveline disconnect clutch remains open,and the DISG is charging a battery and supplying negative drivelinetorque.

Between time T₆₃ and time T₆₄, the DISG transitions from a torquecontrol mode to a speed control mode in response to the increase indriver demand torque. The DISG is then adjusted to a desired speed. TheTCC is also adjusted to provide a constant amount of slip.

At time T₆₄, the driveline disconnect clutch is at least partiallyclosed to start the engine. The DISG torque is increased from a negativetorque toward zero torque and then it goes positive to provide torque tostart the engine. The amount of DISG torque increase depends on theamount of torque used to crank the engine. The engine speed increases asspark and fuel are supplied to the engine as the engine rotates.

Between time T₆₄ and time T₆₅, the engine output torque increases andcombustion torque accelerates the engine. The DISG is transitioned backto braking mode and the driveline disconnect clutch is opened inresponse to combustion in the engine. Opening the driveline disconnectclutch allows the engine to accelerate to the DISG speed withoutaffecting driveline torque.

At time T₆₅, the driveline disconnect clutch is closed in response toengine speed reaching DISG speed. Closing the driveline disconnectclutch after the engine reaches DISG speed may reduce driveline torquedisturbances. Engine torque is also reduced via reducing a throttleopening amount or via adjusting cylinder valve timing.

At time T₆₆, the engine is transitioned to a deceleration fuel shutoffmode where the engine rotates without being fueled and withoutcombusting an air-fuel mixture. The engine provides braking torque whenit rotates without being fueled. The engine braking torque may beadjusted via adjusting intake manifold pressure via a throttle orcylinder valves. The DISG is also transitioned back to torque controlmode.

Thus, the methods and systems of FIGS. 1-3 and 29-30 provide forcontrolling driveline braking, comprising: providing driveline brakingvia an electric machine while rotation of an engine is stopped; andstarting rotation of the engine in response to a battery state of chargeexceeding a threshold. In this way, engine braking may take over forDISG braking when energy storage device charge is greater than athreshold (e.g., fully charged). The method further comprisesautomatically stopping the engine and opening a driveline disconnectclutch between the engine and the electric machine while the engine isstopped, and further comprising providing engine braking torque towheels after starting rotation of the engine and where the drivelinedisconnect clutch is at least partially closed to rotate the engine.

In one example, the method further comprises operating the electricmachine in a speed control mode while converting vehicle kinetic energyinto electrical energy. The method further comprises increasing slip ofa torque converter clutch during starting rotation of the engine whileengine speed is less than an idle speed of the engine. The methodincludes where the engine is rotated via a driveline integratedstarter/generator. The method includes where a driveline disconnectclutch is engaged to couple the engine to the driveline integratedstarter/generator. The method further comprises operating the electricmachine in a speed control mode and adjusting electric machine torque tomaintain driveline speed at a substantially constant torque.

The methods and systems of FIGS. 1-3 and 29-30 also provide forcontrolling driveline braking, comprising: providing driveline brakingvia a first electric machine while rotation of an engine is stopped;starting rotation of the engine in response to a battery state of chargeexceeding a threshold, where rotation of the engine is performed via asecond electric machine. The method includes where the second electricmachine is not coupled to the engine before engine rotation iscommanded. The method includes where the first electric machine is notmechanically coupled to the engine while engine rotation is stopped.

In one example, the method includes where the second electric machine isdisengaged from the engine after engine speed reaches a threshold speed.The method further comprises closing a driveline disconnect clutch whenengine speed is substantially equal to the first electric machine. Themethod further comprises increasing torque converter clutch slip duringclosing the driveline disconnect clutch. The method includes where apower output capacity of the second electric machine is lower than apower output capacity of the first electric machine.

The methods and systems of FIGS. 1-3 and 29-30 also provide for avehicle system, comprising: an engine; a dual mass flywheel (DMF)including a first side mechanically coupled to the engine; a drivelinedisconnect clutch mechanically including a first side coupled to asecond side of the dual mass flywheel; a driveline integratedstarter/generator (DISG) including a first side coupled to a second sideof the driveline disconnect clutch; a starter other than the DISGincluding a base state where the starter is not engaged to the engine; atransmission selectively coupled to the engine via the drivelinedisconnect clutch; and a controller including non-transitoryinstructions executable to automatically stop the engine, providedriveline braking via the DISG while engine rotation is stopped, rotatea stopped engine via the starter other than the DISG when the DISG isproviding driveline braking and when battery state of charge is greaterthan a threshold level.

In some examples, the vehicle system further comprises additionalinstructions to increase slip of a torque converter clutch when thedriveline disconnect clutch is at least partially closed. The vehiclesystem further comprises closing the driveline disconnect clutch afterthe engine is started. The vehicle system includes where the DISG has apower output capacity greater than the starter other than the DISG. Thevehicle system further comprises a torque converter clutch andadditional instructions for increasing slip of torque converter clutchduring closing the driveline disconnect clutch. The vehicle systemincludes where the DISG is supplying charge to an energy storage devicewhen providing driveline braking.

The methods and systems of FIGS. 1-3 and 29-30 also provide forcontrolling driveline braking, comprising: providing driveline brakingvia an electric machine while rotation of an engine is stopped; andadjusting a torque of the electric machine in response to a condition ofengine. The method includes where the condition of the engine is an oiltemperature. The method includes where the condition of the engine is avalve timing of the engine. The method includes where the condition ofthe engine is an engine coolant temperature. The method includes wherethe condition of the engine is an estimated engine brake torque. Themethod includes where the driveling braking is provided via operatingthe electric machine in a generator mode. The method includes where thetorque of the electric machine is varied as the condition of the enginevaries.

The methods and systems of FIGS. 1-3 and 29-30 also provide forcontrolling driveline braking, comprising: providing driveline brakingvia an electric machine while rotation of an engine is stopped; andadjusting a torque of the electric machine based a braking torque of theengine. The method includes where the braking torque of the engine isestimated based on engine oil temperature. The method includes where thebraking torque of the engine is estimated based on a speed of theelectric machine. The method includes where the torque of the electricmachine is a negative torque. The method includes where the electricmachine is in a generator mode. The method includes where the brakingtorque of the engine is a deceleration fuel shut-off braking torque. Themethod includes where the braking torque of the engine is based on aposition of a throttle.

The methods and systems of FIGS. 1-3 and 29-30 also provide for avehicle system, comprising: an engine; a dual mass flywheel (DMF)including a first side mechanically coupled to the engine; a drivelinedisconnect clutch mechanically including a first side coupled to asecond side of the dual mass flywheel; a driveline integratedstarter/generator (DISG) including a first side coupled to a second sideof the driveline disconnect clutch; a starter other than the DISGincluding a base state where the starter is not engaged to the engine; atransmission selectively coupled to the engine via the drivelinedisconnect clutch; and a controller including non-transitoryinstructions executable to automatically stop the engine, providedriveline braking via the DISG while engine rotation is stopped, andadjust a torque of the DISG to an engine brake torque while providingdriveline braking.

In some examples, the vehicle system further comprises additionalinstructions to accelerate the engine to a speed of the DISG. Thevehicle system further comprises additional instructions to reduce anegative torque provided by the DISG in response to a negative torqueprovided by the engine to a driveline. The vehicle system furthercomprises additional instructions for starting the engine via thestarter other than the DISG. The vehicle system further comprisesadditional instructions for stopping combustion in engine cylindersafter starting the engine. The vehicle system further comprisesadditional instructions for adjusting engine braking after stoppingcombustion in engine cylinders.

The methods and systems of FIGS. 1-3 and 29-30 also provide forcontrolling driveline braking, comprising: providing driveline brakingvia an electric machine while rotation of an engine is stopped; andautomatically activating a device to consume charge provided via theelectric machine while the electric machine is providing drivelinebraking. The method includes where the device is activated in responseto a state of charge of an electric storage device exceeding a thresholdlevel.

In one example, the method includes where the device is a heatingdevice. The method includes where the heating device is a windowdefroster. The method includes where the heating device is an emissiondevice heater. The method includes where the device is a pump. Themethod includes where the pump is a fuel injection pump.

The methods and systems of FIGS. 1-3 and 29-30 also provide forcontrolling driveline braking, comprising: providing driveline brakingvia an electric machine while rotation of an engine is stopped; andincreasing current supplied to a device while the electric machine isproviding driveline braking. The method includes where the currentincrease is based on a rate of charge being output by the electricmachine. The method includes where the electric machine is providingcharge to an energy storage device while the electric machine isproviding driveline braking. The method includes where the currentincrease is based on a state of charge of an energy storage device. Themethod includes where the device is a pump. The method includes wheredevice is a heater. The method includes where the device is a light.

The methods and systems of FIGS. 1-3 and 29-30 also provide forcontrolling driveline braking, comprising: providing driveline brakingvia an electric machine while rotation of an engine is stopped;automatically activating a device to consume charge provided via theelectric machine while the electric machine is providing drivelinebraking; rotating the engine in response to a state of charge of anenergy storage device; and stopping to rotate the engine when the stateof charge of the energy storage device is less than a threshold level.

In one example, the method includes where the device to consume chargeprovided via the electric machine is a device having an operating statethat is not visible or audible by the driver. The method includes wherethe device to consume charge provided via the electric machine is aheater. The method includes where the heater provides heat to ambientair. The method includes where the heater provides heat to an exhaustsystem. The method further comprises stopping to provide drivelinebraking via the electric machine when the engine is rotating.

The methods and systems of FIGS. 1-3 and 29-30 also provide forcontrolling driveline braking, comprising: providing driveline brakingvia an electric machine while rotation of an engine is stopped;operating the electric machine in a speed control mode in response to arequest to provide driveline braking via the engine; starting theengine; accelerating the engine to a speed of the electric machine; andclosing an open driveline disconnect clutch in response to engine speedsubstantially equaling electric machine speed. The method includes wherethe engine is started via a starter other than the electric machine.

In some examples, the method includes where the request to providedriveline braking via the engine is based on a state of charge of anenergy storage device. The method includes where the request to providedriveline braking via the engine is in response to the state of chargeof the energy storage device being greater than a threshold amount ofcharge. The method further comprises adjusting slip of a torqueconverter clutch in response to closing the open driveline disconnectclutch. The method includes where the slip of the torque converterclutch is increased. The method includes where the electric machineprovides torque to start the engine.

The methods and systems of FIGS. 1-3 and 29-30 also provide forcontrolling driveline braking, comprising: providing driveline brakingvia an electric machine while rotation of an engine is stopped; startingand rotating the engine; injecting fuel to the engine; accelerating theengine to a speed of the electric machine; and discontinuing to injectfuel to the engine and providing driveline braking via the engine whilethe electric machine outputs less than a threshold amount of current.The method further comprises closing a driveline disconnect clutch inresponse to engine speed substantially equaling electric machine speed.

In one example, the method further comprise operating the electricmachine in a speed control mode during closing the driveline disconnectclutch. The method further comprises increasing slip of a torqueconverter clutch during closing the driveline disconnect clutch. Themethod includes where the engine is started in response to charge of anenergy storage device exceeding a threshold charge. The method includeswhere electric machine torque is reduced in response to engine brakingtorque increasing after discontinuing to inject fuel to the engine. Themethod includes where the engine is started via a starter other than theelectric machine.

The methods and systems of FIGS. 1-3 and 29-30 also provide for avehicle system, comprising: an engine; a dual mass flywheel (DMF)including a first side mechanically coupled to the engine; a drivelinedisconnect clutch mechanically including a first side coupled to asecond side of the dual mass flywheel; a driveline integratedstarter/generator (DISG) including a first side coupled to a second sideof the driveline disconnect clutch; a starter other than the DISGincluding a base state where the starter is not engaged to the engine; atransmission selectively coupled to the engine via the drivelinedisconnect clutch; and a controller including non-transitoryinstructions executable to automatically stop the engine, providedriveline braking via the DISG while engine rotation is stopped, startthe engine in response to a state of charge of an energy storage device,stop combustion in the engine while the engine is rotating, and providedriveline braking via the engine. In this way, the system may converterto electric driveline braking to mechanical driveline braking.

In some examples, the vehicle system further comprises additionalinstructions to accelerate the engine to a speed of the DISG. Thevehicle system further comprises additional instructions to close thedriveline disconnect clutch when engine speed is substantially equal toDISG speed. The vehicle system further comprises additional instructionsfor starting the engine via the starter other than the DISG. The vehiclesystem further comprises additional instructions for stopping combustionin engine cylinders after starting the engine. The vehicle systemfurther comprises additional instructions for adjusting engine brakingafter stopping combustion in engine cylinders.

Referring now to FIG. 31, a flowchart of a method for controllingdriveline lash during vehicle braking provided via the vehicle drivelineis shown. The method of FIG. 31 may be stored as executable instructionsnon-transitory memory in the system of FIGS. 1-3.

At 3102, method 3100 judges whether or not the engine is off and theDISG is in a regeneration mode (e.g., where the DISG is converting thevehicle's kinetic energy into electrical energy). In one example, anengine may be judged to be stopped rotating when engine speed is zero.The DISG may be determined to be in a regeneration mode when currentflows from the DISG and the DISG is providing negative torque to thedriveline. If method 3100 judges that the engine is not rotating and theDISG is in regeneration mode, the answer is yes and method 3100 proceedsto 3104. Otherwise, the answer is no and method 3100 proceeds to exit.

At 3104, method 3100 shifts a transmission to a gear that allows DISGspeed to stay below a base DISG speed. The base DISG speed is a speedbelow which the DISG may provide rated torque (e.g., maximum DISGtorque). If DISG speed is greater than base DISG speed, DISG torque isinversely proportional to DISG speed. Thus, if the DISG speed is greaterthan base DISG speed, the transmission may be upshifted so that DISGspeed is less than DISG base speed. If vehicle speed is such that DISGspeed cannot be reduced to less than DISG base speed by upshifting thetransmission, the transmission may be shifted to a gear that allows theDISG to rotate at a speed closest to DISG base speed. Additionally, insome examples, the DISG may be transitioned into a speed control mode at3104 rather than waiting for an increase in driver demand torque. Method3100 proceeds to 3106 after the transmission is shifted so that DISGspeed is near or less than DISG base speed.

At 3106, method 3100 judges whether or not there is a request forincreased positive driveline torque. A request for increased positivedriveline torque may be in response to an increasing driver demandtorque. The driver demand torque may be determined from an acceleratorpedal or a controller. If method 3100 judges that there is a request forincreased positive driveline torque (e.g., to accelerate the vehicle),the answer is yes and method 3100 proceeds to 3108. Otherwise, theanswer is no and method 3100 returns to 3104.

At 3108, method 3100 adjusts the torque converter clutch (TCC) capacity.In one example, the TCC capacity is adjusted to the desired torqueconverter output torque minus a torque amount the torque converter wouldgenerate with a fully open TCC. The amount of torque the converter wouldgenerate with a fully open TCC may be determined from torque converterimpeller speed and torque converter turbine speed. In particular, thetorque converter impeller speed and the torque converter turbine speedindex a function or table stored in memory that outputs torque convertertorque output based on torque converter impeller speed and torqueconverter turbine speed. Once TCC capacity is determined it is output tothe TCC. Method 3100 proceeds to 3110 after the TCC capacity isadjusted.

At 3110, the DISG is transitioned to a speed control mode from a torquecontrol mode. In speed control mode, DISG torque is adjusted to providea desired DISG speed. The desired DISG speed may be constant or it maychange with vehicle operating conditions. Method 3100 proceeds to 3112after the DISG is transitioned to a speed control mode.

At 3112, method 3100 adjusts DISG speed to adjust the torque converteroutput torque. In particular, torque converter torque is adjusted from anegative torque to a positive torque via adjusting DISG speed. In oneexample, a desired torque converter output torque profile is stored inmemory and retrieved during a transition from driveline braking (e.g.,negative driveline torque) to driveline acceleration (e.g., positivedriveline torque). The desired torque converter output torque profilespecifies torque converter output torque based on change in driverdemand torque and present transmission gear. The desired torqueconverter output torque and turbine speed are input to a function ortable that outputs torque converter impeller speed. The table orfunction describes a torque converter transfer function. The DISG iscommanded to the torque converter impeller speed so that the torqueconverter outputs the desired torque converter output torque. After theDISG completes the desired torque converter output profile, the DISGtorque is adjusted to provide the desired driver demand torque. In thisway, the DISG speed is controlled as a function of torque converterturbine speed and desired torque converter output. Stated in anotherway, the actual torque converter output torque is controlled as afunction of torque converter impeller speed and turbine speed.

In an alternative example, the DISG speed adjusts the torque converteroutput torque by varying torque converter impeller speed relative totorque converter turbine speed. In particular, the DISG increases thetorque converter output torque from a negative torque to a positivetorque via increasing DISG speed. Torque converter output torque isincreased quickly to reduce lash between transmission and drivelinegears. Torque converter output torque is reduced as lash between gearsets is reduced so that gear tooth to gear tooth impact may be reduced.

For example, gear lash crossing gear tooth to gear tooth speed isadjusted by adjusting the torque converter output torque as a functionof estimated gear tooth to gear tooth speed. In one example, gear toothspeed to gear tooth speed is the difference between torque converterturbine speed and either the transmission output speed or the wheelspeed. The speed difference between turbine speed and transmissionoutput speed or wheel speed is relatively small until twist in drivelineshafts is relieved. Positive torque converter output torque is increasedvia increasing DISG speed in response to a small difference in speedbetween the torque converter turbine and the transmission output speedor wheel speed. DISG output speed is increased quickly when thedifference in the torque converter turbine and the transmission outputspeed or wheel speed is small so that gear teeth separate. The speeddifference will increase as gear teeth transition from being in contactto not being in contact. The DISG speed is decreased as the differencein the torque converter turbine and the transmission output speed orwheel speed increases so that impact force between gear sets may bereduced.

In one example, once torque converter impeller speed minus transmissionoutput shaft speed or wheel speed exceeds a threshold speed, the DISGspeed is reduced to decrease tooth to tooth impact force. The DISG speedis increased after the difference between the torque converter turbineand the transmission output speed or wheel speed is less than athreshold speed so that gear teeth remain in contact after thetransition from negative driveline torque to positive driveline torque.Method 3100 proceeds to 3114 after DISG lash adjustment begins.

At 3114, method 3100 judges whether or not gear lash is reduced to lessthan a threshold amount. In one example, gear lash is determined to beless than a threshold amount when positive torque has been applied tothe driveline and a difference between the torque converter turbinespeed and the transmission output speed or wheel speed is less than athreshold level. If method 3100 judges that gear lash is reduced to lessthan a threshold amount, the answer is yes and method 3100 proceeds to3116. Otherwise, the answer is no and method 3100 returns to 3112.

At 3116, method 3100 increases the DISG output torque. Since the DISG isin speed control mode, the DISG output torque may be increased inresponse to driveline torque being transferred to the engine anddecreasing driveline speed. In other words, DISG positive torque may beincreased as DISG speed decreases from the desired DISG speed. Inanother example, DISG torque output may be increased while the DISG isin speed control mode by increasing DISG torque based on drivelinedisconnect clutch torque (e.g., the amount of torque transferred fromthe DISG to the engine via the DISG). The desired driveline disconnectclutch torque may be stored in memory in a function or table and thetorque increase is applied to the DISG during and engine restart inresponse to disconnect clutch closing. Method 3100 proceeds to 3118after DISG output torque is adjusted to start the engine.

At 3118, method 3100 restarts the engine. The engine is restarted via atleast partially closing the driveline disconnect clutch and supplyingspark and fuel to the engine. In some examples, closing the drivelinedisconnect clutch and increasing DISG output torque may occursimultaneously so that any driveline torque disturbance may be reduced.Method 3100 proceeds to 3120 after engine starting commences.

At 3120, method 3100 rejects engine torque disturbances that may bedelivered to the driveline. For example, during engine starting, theengine may consume driveline torque so as to accelerate during starting.The engine torque disturbances may be rejected in response to a changein driveline speed at the DISG. Since the DISG is in speed control modeand following a desired speed, DISG torque may be increased when theengine consumes driveline torque and decelerates the driveline.Additionally, if the engine accelerates and delivers torque to thedriveline after starting, DISG torque may be decreased so that the nettorque supplied to the driveline via the DISG and engine remainssubstantially constant (e.g., ±30 Nm). In this way, the driveline speedmay be controlled in a closed loop fashion via adjusting DISG torque.

In another example, driveline torque disturbances may be rejected viaopen loop DISG torque adjustments. For example, when the disconnectclutch begins to close, the DISG torque may be increased while the DISGis in speed control mode. In particular, DISG torque may be adjusted viaadding the driveline disconnect clutch torque to the DISG torquecommand. The DISG torque command is further adjusted in response to theDISG speed. Thus, if the driveline disconnect clutch torque is under oroverestimated, the DISG speed control loop will eliminate the error indriveline disconnect torque that was added to the DISG torque. Thedriveline torque disturbances rejected during engine starting may berejected between the time engine cranking begins until the enginereaches DISG speed and the driveline disconnect clutch is fully closed.Method 3100 proceeds to 3122 after driveline disturbances during enginestarting are rejected.

At 3122, method 3100 provides the desired torque to the driveline. Thedesired torque may be provided solely via the DISG, solely via theengine, or via the engine and the DISG. In one example, DISG torque andengine torque are provided as fractions of a driver demand torque asdetermined from an accelerator pedal. For example, if driver demandtorque is determined to be 100 N-m at the torque converter impeller theengine may provide 80% of the driver demand torque or 80 N-m while theDISG provides 20% or 20 N-m so that 100 N-m is provided to the torqueconverter impeller. Method 3100 proceeds to exit after the desiredtorque is provided to the driveline.

It should be noted that in some examples, 3116-3120 may occur at thesame time as 3108-3114 so that driveline torque may be more responsiveto driver demand torque. Shifting the transmission to a gear that allowsthe DISG to operate below base DISG speed may increase the possibilitythat the DISG has the torque capacity to restart the engine and mitigategear impact from driveline gear lash simultaneously.

Referring now to FIG. 32, an example sequence for reducing gear lashimpact of a driveline according to the method of FIG. 31 is shown. Thesequence of FIG. 32 may be provided by the system of FIGS. 1-3.

The first plot from the top of FIG. 32 represents vehicle speed versustime. The Y axis represents vehicle speed and vehicle speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The second plot from the top of FIG. 32 represents driver demand torqueversus time. The Y axis represents driver demand torque and driverdemand torque increases in the direction of the Y axis arrow. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The third plot from the top of FIG. 32 represents engine state versustime. The Y axis represents engine state and the engine is rotating whenthe engine state trace is at a higher level. The engine has stoppedrotating when the engine state trace is at a lower level. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The fourth plot from the top of FIG. 32 represents torque converterclutch (TCC) duty cycle versus time. The Y axis represents TCC dutycycle and TCC duty cycle increases in the direction of the Y axis arrow.The X axis represents time and time increases from the left hand side ofthe figure to the right hand side of the figure. The TCC closing forceincreases as the TCC duty cycle increases. The TCC may transfer lesstorque between the DISG and the transmission as the TCC duty cycleincreases because the torque converter torque multiplication may bereduced. The TCC is locked (e.g., torque converter impeller speed equalstorque converter turbine speed) when the TCC trace is near the Y axisarrow.

The fifth plot from the top of FIG. 32 represents transmission gearversus time. The Y axis represents transmission gear and specifictransmission gears are indicated along the Y axis. The X axis representstime and time increases from the left hand side of the figure to theright hand side of the figure.

The sixth plot from the top of FIG. 32 represents DISG speed versustime. The Y axis represents DISG speed and DISG speed increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure. Horizontal line 3202 represents base DISG speed.

At time T₆₈, vehicle speed is at an elevated level as is the driverdemand torque. The engine is operating and combusting air-fuel mixtures.The TCC is locked as indicated by the TCC duty cycle being near the Yaxis label. The transmission is in fifth gear and the DISG speed is at amedium level and above the DISG base speed 3202.

At time T₆₉, the driver demand torque is reduced to a low value inresponse to a driver releasing an accelerator pedal, for example. Thevehicle speed, driver demand torque, engine state, TCC duty cycle,transmission gear, and DISG speed remain at similar levels as at timeT₆₈. However, the DISG transitions from producing positive torque andconsuming electrical energy to producing negative torque and generatingelectrical energy. Fuel and spark delivery to the engine are alsostopped so that the engine decelerates but continues to rotate withoutreceiving fuel.

Between time T₆₉ and time T₇₀, vehicle speed decreases as does DISGspeed. The engine continues to rotate as indicated by the engine statestaying at a higher level, and the TCC duty cycle also remains at ahigher level where the TCC is locked. The transmission remains in 5^(th)gear and the driver demand torque remains at a lower level.

At time T₇₀, engine rotation is stopped in response to the low driverdemand torque as indicated by the engine state flag transitioning to alower level. The driveline disconnect clutch (not shown) is opened andthe DISG is transitioned to a speed control mode in response to stoppingthe engine. The DISG speed and vehicle speed continue to be reduced, andthe transmission remains in 5^(th) gear.

Between time T₇₀ and time T₇₁, vehicle speed and DISG speed continue todecrease. In this example, the transmission downshifts when downshiftingwill allow the DISG speed to remain under base DISG speed. The DISGspeed is commanded to a speed based on driver demand torque, vehiclespeed, and selected gear. For example, the transmission is held in5^(th) gear and DISG speed is reduced to less than base DISG speed. DISGspeed continues to decrease to a threshold speed at which the DISG willbe below DISG base speed if the transmission is shifted into 4^(th)gear. The transmission is downshifted to 4^(th) gear when DISG speed isless than the threshold speed and DISG speed is increased to a speedthat is based on DISG speed before the shift and the new gear ratio.

In some examples during the beginning of vehicle deceleration or areduction in driver demand torque, the present DISG speed may be greaterthan DISG base speed. In these cases, the transmission may be upshiftedat the beginning of vehicle deceleration or in response to the decreasein driver demand torque so that DISG speed is reduced to less than DISGbase speed. By reducing DISG speed to less than DISG base speed, it maybe possible to provide torque from the DISG to restart the engine toreduce gear tooth to gear tooth impact that is due to gear lash. Thetransmission gears are downshifted at times that allow the DISG speed toremain less than DISG base speed.

The TCC duty cycle is also reduced in response to driveline disconnectclutch state (not shown), vehicle speed, and driver demand torque. TheTCC application force and TCC duty cycle are modulated to reduce anytorque disturbance through the driveline that may result from openingthe driveline disconnect clutch. The engine remains stopped as indicatedby the engine state being at a lower level. The driver demand torquealso remains low.

It should also be mentioned that driveline gear teeth may havetransitioned from transmitting torque from front faces of gear teeth torear faces of gear teeth as the driveline transitions from producingpositive torque to providing a negative or braking torque. Gear tooth togear tooth impact may result when the driveline transitions back toproducing positive torque if the transitions is not managed in a desiredmanner.

At time T₇₁, the driver demand torque is increased in response to driveror controller input. The DISG speed is increased so as to separate teethin the driveline. The DISG is accelerated as a function of gear tooth togear tooth speed difference. In particular, the DISG is accelerated at ahigher rate when gear teeth are at the same speed so as to separate theteeth.

At time T₇₂, the DISG acceleration is reduced and the DISG maydecelerate as the speed difference between gear teeth increases.Decelerating the DISG may reduce gear tooth to gear tooth impact forcesby lowering the velocity between gear teeth. Shortly after time T₇₂, theDISG acceleration is increased after the space or lash between gearteeth has been removed. By waiting to accelerate the DISG until afterthe gear teeth are in contact, it may be possible to reduce drivelinetorque disturbances and provide smoother negative to positive torquetransitions. The TCC slip and application force between time T₇₁ andtime T₇₃ is also adjusted and/or modulated to reduce torque disturbancesin the driveline. Torque from the DISG begins to accelerate the vehicleand the DISG is transitioned into a torque control mode.

At time T₇₃, spark and fuel are supplied to the engine and the drivelinedisconnect clutch is closed so that the engine is started. The TCC dutycycle and application force are modulated to reduce any torquedisturbance in the driveline that may result from closing the drivelinedisconnect clutch during engine starting. The TCC is locked after theengine is started so as to improve driveline efficiency. Further, thetransmission begins shifting through gears to accelerate the vehicle.

In this way, lash and impact between driveline gear teeth may be reducedwhen a driveline is transitioned from a braking mode to a torqueproducing mode. By adjusting DISG speed and torque in this way, it maybe possible to reduce driveline torque disturbances that may be apparentto a driver.

Thus, the methods and systems of FIGS. 1-3 and 31-32 provide forcontrolling driveline lash, comprising: shifting a transmission to agear that permits an electric machine that is coupled to thetransmission to operate at a lower speed than a base speed of theelectric machine in response to a decrease in a driver demand torque;and reducing gear tooth to gear tooth impact via operating the electricmachine in a speed control mode during a driveline torque transitionfrom a negative torque to a positive torque. The method furthercomprises reducing a torque converter clutch application force duringthe driveline torque transition from the negative torque to the positivetorque. The method further comprises stopping rotation of an engine inresponse to the decrease in driver demand torque.

In one example, the method further comprises opening a drivelinedisconnect clutch in response to the decrease in driver demand torque.The method further comprises adjusting speed of the electric machine inresponse to a difference in speed between a first gear tooth and asecond gear tooth during the driveline torque transition from thenegative torque to the positive torque. The method further comprisesdownshifting the transmission in response to vehicle speed. The methodincludes where the electric machine is operated in a torque control modeimmediately before operating the electric machine in the speed controlmode during the driveline torque transition from the negative torque tothe positive torque.

The methods and systems of FIGS. 1-3 and 31-32 also provide forcontrolling driveline lash, comprising: reducing gear tooth to geartooth impact via operating an electric machine in a speed control modeduring a driveline torque transition from a negative torque to apositive torque; and accelerating the electric machine to separate afirst gear tooth and a second gear tooth during the driveline torquetransition from the negative torque to the positive torque. The methodfurther comprises decelerating the electric machine in response to anincrease in a speed difference between the first gear tooth and thesecond gear tooth. The method further comprises accelerating theelectric machine in response to a decrease in the speed differencebetween the first gear tooth and the second gear tooth afterdecelerating the electric machine.

In one example, the method includes where the transition from thenegative torque to the positive torque is in response to an increase indriver demand torque. The method further comprises opening a drivelinedisconnect clutch that is mechanically coupled to the electric machinebefore reducing the gear tooth to gear tooth impact in response to adecrease in driver demand torque. The method further comprises reducinga torque converter clutch application force in response to a decrease indriver demand torque before reducing the gear tooth to gear toothimpact. The method includes where the electric machine speed iscontrolled as a function of a speed difference between a first geartooth and a second gear tooth.

The methods and systems of FIGS. 1-3 and 31-32 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller includingnon-transitory instructions executable to automatically stop enginerotation, reduce a gear tooth to gear tooth impact via operating theDISG in a speed control mode during a driveline torque transition from anegative torque to a positive torque, and to start engine rotation whilereducing the gear tooth to gear tooth impact.

In one example, the vehicle system includes where engine rotation isstarted via closing the driveline disconnect clutch. The vehicle systemfurther comprises additional instructions to adjust a torque converterclutch application force while reducing the gear tooth to gear toothimpact. The vehicle system further comprises additional instructions toopen the driveline disconnect clutch in response to a driver demandtorque. The vehicle system further comprises additional instructions toat least partially close the driveline disconnect clutch to start theengine in response to a driver demand torque. The vehicle system furthercomprises additional instructions shift the transmission to a gear thatrotates the DISG at a speed less than the DISG base speed during vehicledeceleration.

Referring now to FIG. 33, a flowchart of a method for transitioningvehicle braking from a driveline to friction brakes is shown. The methodof FIG. 33 may be stored as executable instructions non-transitorymemory in the system of FIGS. 1-3.

Referring now to 3302, method 3300 estimates vehicle mass and roadgrade. In one example, road grade may be estimated or determined via aninclinometer. Vehicle mass may be determined as described at 904 ofmethod 900. Method 3300 proceeds to 3304 after vehicle mass and roadgrade are determined.

At 3304, method 3300 judges whether or not the vehicle is deceleratingor if a driver has reduced a driver torque demand. In one example,vehicle deceleration may be determined via decreasing vehicle speed. Areduced driver demand torque may be determined from a release of anaccelerator pedal. If method 3300 judges that vehicle deceleration orreduced driver demand is present, the answer is yes and method 3300proceeds to 3306. Otherwise, the answer is no and method 3300 proceedsto exit.

At 3306, method 3300 judges whether or not state of charge (SOC) of anenergy storage device is less than a threshold amount of charge. In oneexample, SOC may be determined via measuring battery voltage. If energystorage device SOC is less than a threshold amount of charge, the answeris yes and method 3300 proceeds to 3308. Otherwise, the answer is no andmethod 3300 proceeds to 3312.

At 3308, method 3300 stops engine rotation and opens the drivelinedisconnect clutch. The engine is stopped via discontinuing to supply theengine with spark and fuel. Method 3300 proceeds to 3310 after enginerotation is stopped and the driveline disconnect clutch is opened.

At 3310, method 3300 operates the DISG in generator mode and charges theenergy storage device. The DISG provides a negative torque to thevehicle driveline in generator mode. In one example, the amount ofnegative torque the DISG provides to the driveline may be adjusted inresponse to vehicle speed and driver demand torque. In another example,the amount of negative torque the DISG provides to the DISG may beadjusted to an estimated braking torque of the engine as describe hereinat the present operating conditions. The rate of vehicle decelerationmay also be stored in memory at 3310. Method 3300 returns to 3304 afterthe DISG begins to charge the energy storage device.

At 3312, method 3300 begins to reduce the negative DISG torque. Further,in some examples, the driveline disconnect clutch may be closed so thatthe engine may provide driveline braking. In one example, the negativeDISG torque is reduced toward zero torque in response to an amount oftorque transferred to the engine via the driveline disconnect clutch.The reduction in DISG negative torque is based on a reduction incharging current. Method 3300 proceeds to 3314 after the DISG torquebegins to be reduced.

At 3314, method 3300 estimates wheel torque via the present road gradeand vehicle deceleration. The wheel torque may be estimated based on thefollowing equations:

F = m ⋅ a $\frac{T\_ wh}{R\_ rr} = F$

so that,

T _(—) wh=m·a·R _(—) rr+R _(—) rr·g·m·sin(Θ)

Where F is equal to force to accelerate/decelerate the vehicle, m isvehicle mass, R_rr is rolling radius of the wheel, a represents vehicleacceleration, g is acceleration due to gravity, and e is the angle ofthe road. Method 3300 proceeds to 3318 after wheel torque is determined.

At 3316, method 3300 adjusts brake supply oil pressure in response tovehicle wheel torque and the decrease in negative DISG torque (e.g.,toward zero DISG torque). In particular, method 3300 simultaneouslyramps up oil pressure supplied to the vehicle's friction brakes andreduces DISG negative torque. The vehicle friction brake force isincreased at a rate that balances the reduction in DISG negative torqueto provide an equivalent rate of vehicle deceleration. In one example,an open loop brake line oil pressure, which may be related to brakeapplication force, is retrieved from a table or function that includesempirically determined brake line oil pressures in response to a desiredwheel braking torque. The desired wheel braking torque provided by thefriction brakes is the wheel torque from 3314 minus the reduction inDISG torque multiplied by the present transmission gear ratio and axleratio. The brake line oil pressure is ramped up to the pressure thatprovides the desired wheel braking torque. In this way, close loopcontrol over vehicle braking may be achieved based on wheel torque.Additionally, in some examples, the driveline disconnect clutch may beclosed and the engine rotated without fuel to provide driveline brakingtorque in response to the decrease in DISG torque and other operatingconditions. Method 3300 proceeds to 3318 after beginning to ramp upbrake line oil pressure and after beginning to ramp down DISG negativetorque.

In other examples, brake line oil pressure may be increased by an openloop estimate of brake application force and the brake application forcemay be further adjusted based on a difference between desired vehiclespeed and actual vehicle speed. In this way, vehicle speed differencemay be a closed loop parameter for adjusting friction braking force.

At 3318, method 3300 judges whether or not there is a brake request fromthe driver. In one example, a brake request from a driver may bedetermined from a position of a brake pedal. If method 3300 judges thatthere is a brake request from a driver, the answer is yes and method3300 proceeds to 3320. Otherwise, the answer is no and method 3300proceeds to 3322.

At 3320, brake line oil pressure is increased in response to driverdemand input. In one example, brake line oil pressure to friction brakesis increased in proportion to displacement of a brake pedal. Method 3300proceeds to 3322 after brake line oil pressure is increased in responseto the driver brake command.

At 3322, method 3300 judges whether or not the vehicle is stopped. Thevehicle may be judged stopped when vehicle speed is zero. If the vehicleis judged to be stopped, the answer is yes and method 3300 exits. If thevehicle is judged to be moving, the answer is no and method 3300 returnsto 3312.

Referring now to FIG. 34, an example sequence for transitioning vehiclebraking from a driveline to friction brakes according to the method ofFIG. 33 is shown. The sequence of FIG. 34 may be provided by the systemof FIGS. 1-3.

The first plot from the top of FIG. 34 represents vehicle speed versustime. The Y axis represents vehicle speed and vehicle speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The second plot from the top of FIG. 34 represents driveline disconnectclutch state versus time. The Y axis represents driveline disconnectclutch state and the driveline disconnect clutch is closed when thedriveline disconnect clutch state trace is near the Y axis arrow. Thedriveline disconnect clutch is open when the driveline disconnect clutchstate trace is near the X axis. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The third plot from the top of FIG. 34 represents engine state versustime. The Y axis represents engine state and the engine is rotating whenthe engine state trace is at a higher level. The engine has stoppedrotating when the engine state trace is at a lower level. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The fourth plot from the top of FIG. 34 represents battery state ofcharge (SOC) versus time. The Y axis represents battery SOC and SOCincreases in the direction of the Y axis arrow. The X axis representstime and time increases from the left hand side of the figure to theright hand side of the figure.

The fifth plot from the top of FIG. 34 represents DISG torque versustime. The Y axis represents DISG torque and DISG torque may be positiveor negative. The X axis represents time and time increases from the lefthand side of the figure to the right hand side of the figure.

The sixth plot from the top of FIG. 34 represents brake line oilpressure of friction brakes versus time. The Y axis represents brakeline oil pressure and brake line oil pressure increases in the directionof the Y axis arrow. The X axis represents time and time increases fromthe left hand side of the figure to the right hand side of the figure.

The seventh plot from the top of FIG. 34 represents vehicle wheel torqueversus time. The Y axis represents vehicle wheel torque and vehiclewheel torque increases in the direction of the Y axis arrow. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

At time T₇₄, vehicle speed is elevated, the engine is operating, and thedriveline disconnect clutch is closed. The battery SOC is relatively lowand decreasing as the DISG provides positive torque to the driveline.The friction brakes are not applied as indicated by the brake line oilpressure being at a low level. The wheel torque is positive.

At time T₇₅, the driver releases the accelerator pedal (not shown).Shortly thereafter, the DISG torque transitions from positive tonegative in response to low driver demand torque from the acceleratorpedal. By transitioning to a negative torque, the DISG providesdriveline braking to slow the vehicle. Further, the DISG generatescharge and supplies the charge to the battery as indicated by theincreasing battery SOC. The friction brake line pressure remains at alow level indicating that the friction brakes are not applied. The wheeltorque transitions from positive torque to negative torque in responseto the DISG transitioning to providing negative torque. Additionally,the driveline disconnect clutch is opened and engine rotation isstopped. The engine is stopped to conserve fuel and the disconnectclutch is opened so that the DISG may provide all driveline braking. Theamount of driveline braking the DISG provides may be empiricallydetermined and stored in memory as a function of vehicle speed anddriver demand torque.

In this example, the driver does not apply the brake pedal afterreleasing the accelerator pedal. However, in some examples, the drivermay apply the brakes after releasing the accelerator pedal. In suchexamples, the brake line pressure may increase in response to thedriver's brake command.

Between time T₇₅ and time T₇₆, the DISG negative torque graduallyincreases until a desired driveline braking torque is established. Thenegative wheel torque also increases as the driveline braking torqueincreases. The driver does not apply the brake pedal and the battery SOCincreases. The driveline disconnect clutch remains open and engine staysin a stopped state.

At time T₇₆, the battery SOC reaches a threshold amount (e.g., fullycharged) in response to the DISG providing charge to the battery. DISGnegative torque is decreased and the amount of charge delivered to thebattery is reduced. The brake line oil pressure is also increased sothat wheel brake torque may be maintained via the friction brakes. Thebrake line oil pressure is increased based on the decrease in DISGnegative torque. In one example, the friction braking force is adjustedbased on wheel torque and the decrease in DISG torque. In some otherexamples, friction brake force applied to slow wheel rotation may beadjusted based on a difference between a desired vehicle speed and anactual vehicle speed. The vehicle speed continues to decrease and thedriveline disconnect clutch remains open. Further, the engine remainsstopped.

At time T₇₇, the driveline disconnect clutch is closed and the engine isrotated without fuel being injected in response to DISG negative torquebeing reduced and in response to operating conditions. For example, theengine may be rotated in response to the reduction in DISG torque and atime since the change in DISG torque. The engine is rotated without fuelto provide braking torque. And, engine braking torque may be adjustedvia activating and deactivating valves and/or adjusting intake manifoldpressure via a throttle and/or valves. The brake line oil pressure isreduced in response to the driveline braking torque that is provided bythe engine. Specifically, the brake line oil pressure is reduced by anamount that reduces torque supplied by friction brakes such thatequivalent vehicle braking is provided even though driveline braking isincreased via rotating the engine without fuel.

At time T₇₈, vehicle speed is approaching zero speed. The drivelinedisconnect clutch is opened and engine rotation is stopped in responseto vehicle speed being reduced to a threshold vehicle speed. The batterySOC remains at a higher level since the DISG is not providing positivetorque to the driveline and draining battery charge. The brake line oilpressure increases as engine braking stops. The increase in brake lineoil pressure increases the force applied by the friction brakes to thewheels.

At time T₇₉, the vehicle speed reaches zero and the wheel torque andbrake line oil pressure are reduce to zero. In some examples, brake lineoil pressure may be maintained when vehicle speed reaches zero so thatthe vehicle stays at zero speed until the driver increases the driverdemand torque via the accelerator pedal. The engine remains stopped andthe driveline disconnect clutch remains in an open state.

In this way, friction brakes may be applied to slow a vehicle whendriveline braking is reduced in response to battery SOC. Further, enginerotation may be stopped and started to further control drivelinebraking. The friction brakes may be applied based on an estimated wheeltorque and/or a difference between desired vehicle speed and actualvehicle speed.

Thus, the methods and systems of FIGS. 1-3 and 33-34 provide for vehiclebraking, comprising: providing driveline braking torque to a vehiclewithout applying friction braking torque to the vehicle; and reducingdriveline braking torque while increasing friction braking torque to thevehicle in response to an energy storage device state of charge, thefriction braking torque is increased by the same amount the drivelinebraking torque is reduced. In this way, the vehicle may transition fromdriveline braking to friction braking in a manner that may be lessnoticeable to a driver.

In one example, the method includes where a rate that the drivelinebraking torque is reduced is equivalent to a rate the friction brakingtorque is increased. The method includes where an engine of the vehicleis not rotating while providing driveline braking torque to the vehicle.The method includes where a driveline disconnect clutch is open whileproviding driveline braking torque. The method includes where thedriveline braking torque is provided in response to a driver demandtorque that is less than a threshold torque. The method includes wherethe friction braking torque is further increased in response to a driverbrake demand.

The methods and systems of FIGS. 1-3 and 33-34 also provide for vehiclebraking, comprising: providing driveline braking torque to a vehiclewithout applying friction braking torque to the vehicle; estimatingvehicle wheel torque; and reducing driveline braking torque whileincreasing friction braking torque to the vehicle in response to theestimated vehicle wheel torque and energy storage device state ofcharge. The method includes where the friction braking torque isincreased in response to the estimated vehicle wheel torque. The methodincludes where the estimated vehicle wheel torque is based on anestimated vehicle mass.

In some examples, the method includes where the estimated vehicle wheeltorque is based on vehicle acceleration. The method further comprisesrotating an engine without fueling the engine. The method furthercomprises adjusting the friction braking torque in response to anestimate of engine braking torque. The method includes where an engineof the vehicle is stopped.

The methods and systems of FIGS. 1-3 and 33-34 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; friction brakes; and a controllerincluding non-transitory instructions executable to automatically stopengine rotation, provide a driveline braking torque via the DISG, andapply the friction brakes while reducing the driveline braking torque.

In one example, the vehicle system includes further instructions toapply the friction brakes based on an estimated wheel torque. Thevehicle system further comprising additional instructions to reduce thedriveline braking torque in response to an energy storage device stateof charge. The vehicle system includes where the driveline brakingtorque is reduced in response to the energy storage device state ofcharge being greater than a threshold amount of charge. The vehiclesystem includes further instructions to apply the friction brakes basedon vehicle speed. The vehicle system includes where the friction brakesare applied via increasing brake line oil pressure. The vehicle systemfurther comprises additional instructions to reduce friction brakeapplication force in response to a vehicle speed of zero.

Referring now to FIG. 35, a flowchart of a method for reducing drivelingtorque disturbances related to gear lash when transitioning fromdriveline braking to vehicle acceleration while a transmission gearchange does not occur. The method of FIG. 35 may be stored as executableinstructions non-transitory memory in the system of FIGS. 1-3.

At 3502, method 3500 judges whether or not the vehicle is deceleratingor if the driver has at least partially released the accelerator pedal.Method 3500 may judge that the vehicle is decelerating via monitoringvehicle speed. Method 3500 may judge that the driver has at leastpartially released the accelerator pedal in response to acceleratorpedal position. If method 3500 judges that the driver has partiallyreleased the accelerator pedal or the vehicle is decelerating, theanswer is yes and method 3500 proceeds to 3504. Otherwise, the answer isno and method 3500 proceeds to exit.

At 3504, method 3500 determines a desired amount of vehicle brakingtorque. The desired amount of vehicle braking torque may be empiricallydetermined and stored in a function or table in memory that is indexedvia vehicle speed and driver demand torque. Thus, the amount of vehiclebraking torque may vary during vehicle deceleration. In one example, thevehicle braking torque is an amount of braking provided at vehiclewheels. Method 3500 proceeds to 3506 after the desired amount of vehiclebraking torque is determined.

At 3506, method 3500 stops engine rotation and opens the drivelinedisconnect clutch to conserve fuel and so that a higher level ofdriveline braking may be provided via the DISG. A greater amount ofdriveline braking via the DISG may allow the energy storage device orbattery to be recharged at a higher rate. The torque converter clutch(TCC) is adjusted to a locked state so that the DISG may be providedadditional energy during vehicle deceleration. Method 3500 proceeds to3508 after the engine is stopped, the driveline disconnect clutchopened, and the TCC locked.

At 3508, method 3500 judges whether or not the energy storage device orbattery state of charge (SOC) is greater than a threshold amount ofcharge. If method 3500 judges that the energy storage device SOC isgreater than a threshold SOC, the answer is yes and method 3500 proceedsto 3512. Otherwise, the answer is no and method 3500 proceeds to 3510.

At 3510, method 3500 applies friction brakes via increasing brake lineoil pressure. Brake line oil pressure may be increased via a pump. Thefriction brakes apply a force that is based on the desired vehiclebraking torque. In one example, a table or function outputs a brake lineoil pressure that is estimated to provide the force that provides thedesired vehicle braking torque. In some examples, the brake linepressure may be adjusted in response to estimated wheel torque or adifference between desired and actual vehicle speed as described herein.Method 3500 proceeds to exit after the friction brakes are adjusted.

At 3512, method 3500 enters a regeneration mode where the DISG providesnegative driveline torque and charges an energy storage device. Inparticular, the negative torque output by the DISG is adjusted toprovide the desired vehicle braking torque including adjustments fortransmission gear selection. In one example, the DISG negative torquemay be adjusted via adjusting DISG charging current. Method 3500proceeds to 3514 after DISG negative torque is adjusted to provide thedesired vehicle braking torque.

At 3514, method 3500 judges whether or not a positive driveline torquehas been requested. A positive driveline torque may be requested via adriver depressing an accelerator pedal (e.g., increase in driver demandtorque) or via a controller. If method 3500 judges that a positivedriveline torque has been requested, the answer is yes and method 3500proceeds to 3516. Otherwise, the answer is no and method 3500 returns to3508.

At 3516, method 3500 increases torque converter clutch (TCC) slip viareducing the TCC application force. In one example, a duty cyclesupplied to an electrical actuator is reduced to reduce the TCCapplication force. The TCC slip may be increased to a predeterminedamount of empirically determined slip. In one example, the TCC slip isbased on the amount of desired driveline torque increase. Method 3500proceeds to 3518 after the TCC slip is increased.

At 3518, the amount of regenerative braking is decreased via reducingDISG negative torque. The regenerative braking torque is reduced towardzero DISG torque output. Method 3500 proceeds to 3520 after beginning todecrease the regenerative braking torque.

At 3520, method 3500 judges whether or not the regenerative brakingtorque is within a predetermined torque range of zero torque (e.g., ±2N-m). In one example, the regenerative braking torque may be estimatedbased on DISG charging current. If method 3500 judges that regenerativebraking torque is within a predetermined torque range of zero torque,the answer is yes and method 3500 proceeds to 3522. Otherwise, theanswer is no and method 3500 returns to 3518 where regenerative brakingis decreased further.

At 3522, method 3500 transitions from operating the DISG in torquecontrol mode to operating the DISG in speed control mode. The DISG speedis set to a speed that is a speed that is a predetermined speed greaterthan the torque converter turbine speed. Since the DISG is coupled tothe torque converter impeller, the torque converter impeller speed isgreater than the torque converter turbine speed. By adjusting DISG speedto a speed greater than the turbine speed, a small positive torque istransmitted through the torque converter to the transmission inputshaft. The small positive torque removes lash between transmission gearsand axle gears so that impact between gears may be reduced. The DISG iscommanded to the predetermined speed for a predetermined amount of timeor until a speed differential between a first gear and a second gear iszero. The speed between the gears may be determined from thetransmission input shaft speed and the transmission output shaft speed.

DISG speed is increased after the DISG has operated at the predeterminedspeed for a predetermined amount of time or after the speed differencebetween gears is zero. In one example, the DISG speed is increased basedon a torque converter model. In particular, torque converter turbinespeed and the desired amount of torque to transmit through the torqueconverter index one or more functions that output a DISG speed thatprovides the desired amount of torque. The desired amount of torque isbased on the driver demand torque. Method 3500 proceeds to 3524 afterthe DISG speed is adjusted and the gear lash is removed.

At 3524, method 3500 remains in speed control mode and DISG current isadjusted based on an estimated amount of torque to start the engine. Aspreviously described, when the DISG is in speed control mode, currentsupplied to the DISG is adjusted based on an error between a desiredDISG speed and an actual DISG speed. Additionally at 3524, DISG currentis increased in response to closing the driveline disconnect clutch torotate and start the engine. In one example, an increase in DISG currentis based on a driveline disconnect clutch transfer function that outputsa torque amount based on application force applied to the drivelinedisconnect clutch. For example, if the transfer function indicates thatthe driveline disconnect clutch is transferring 25 N-m at the presentapplication force, the DISG current is increased to a level thatprovides an additional 25 N-m of positive torque. The drivelinedisconnect clutch application force may follow an empirically determinedtrajectory that is stored in controller memory. In this way, an openloop current based on the driveline disconnect clutch application forceis provided to the DISG so that DISG speed varies less and so that theclosed loop DISG speed controller may provide less speed correction.Method 3500 proceeds to 3526 after DISG speed and torque are adjusted.

At 3526, method 3500 starts the engine. The engine is started viasupplying spark and fuel to the engine as the engine rotates. The engineis accelerated to the DISG speed and then the driveline disconnectclutch is closed. Engine torque and/or DISG torque are provided to thedriveline after the driveline disconnect clutch is closed. The DISG alsotransitions from speed control mode to torque control mode after thedriveline disconnect clutch is closed.

Referring now to FIG. 36, an example sequence for reducing gear lashimpact of a driveline according to the method of FIG. 35 is shown. Thesequence of FIG. 36 may be provided by the system of FIGS. 1-3.

The first plot from the top of FIG. 36 represents engine speed versustime. The Y axis represents engine speed and engine speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure. Horizontal line 3602 represents the speed of a torqueconverter impeller during the present sequence.

The second plot from the top of FIG. 36 represents pedal positions (e.g.accelerator pedal 3606 (driver demand torque) and brake pedal 3604)torque versus time. The Y axis represents pedal position and pedalposition increases in the direction of the Y axis arrow. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The third plot from the top of FIG. 36 represents torque converterclutch capacity (TCC) versus time. The Y axis represents TCC capacityand TCC capacity increases in the direction of the Y axis arrow. The Xaxis represents time and time increases from the left hand side of thefigure to the right hand side of the figure.

The fourth plot from the top of FIG. 36 represents driveline disconnectclutch state versus time. The Y axis represents driveline disconnectclutch state and driveline disconnect clutch state is fully applied whenthe trace is at a higher level near the Y axis arrow. The drivelinedisconnect clutch is released when the driveline disconnect clutch statein near the X axis. The driveline disconnect application pressureincreases as the driveline disconnect clutch state increases. Further,the amount of torque transmitted across the driveline disconnect clutchincreases as the driveline disconnect clutch state trace levelincreases. The X axis represents time and time increases from the lefthand side of the figure to the right hand side of the figure.

The fifth plot from the top of FIG. 36 represents driveline integratedstarter/generator (DISG) torque versus time. The Y axis represents DISGtorque and DISG torque increases in the direction of the Y axis arrow.The X axis represents time and time increases from the left hand side ofthe figure to the right hand side of the figure.

The sixth plot from the top of FIG. 36 represents transmission torque atthe transmission input shaft versus time. The Y axis representstransmission input shaft torque and transmission input shaft torqueincreases in the direction of the Y axis arrow. The X axis representstime and time increases from the left hand side of the figure to theright hand side of the figure.

FIG. 36 shows one example operation of an engine restart with modulatedtorque converter clutch operation to control transition through thetransmission gear lash region (e.g., zero torque through thetransmission) while maintaining transmission gear. One example includesa method where, the driveline disconnect clutch is engaged upon tip-in(e.g., depression of the accelerator pedal), and where the DISG spinsthe engine up to at least cranking speed (e.g., 250 RPM). Engine fuelingand combustion provide torque to accelerate the engine while the enginespeed continues to rise via DISG torque (as opposed to a starter motortype start). Such operation provides rapid engine torque for driving thevehicle. However, since such rapid increase in torque may cause clunkthrough the gear lash zone, the torque converter clutch is at leastpartially opened and optionally modulated to control the transitionthrough the gear lash zone and reduce the rate of rise of wheel torque,until after transitioning through the gear lash zone. Additionally, theDISG output torque can be adjusted to control the driveline torqueoutput during the transition through the gear lash zone.

Additional details of the adjustments made with regard to gear lashcrossing, that may be used in the lash crossing control described above,are now described. As explained herein, the engine may be shutdown, andthe driveline disconnect clutch opened when the vehicle is coming to astop, stopped, or moving/driving when the torque from the DISG issufficient to accelerate the vehicle and meet demanded torque, overcomethe road load, as shown at time T₈₀.

Specifically, during events when the operator is not requestingdriveline torque (e.g., closed accelerator pedal events), and the engineis not rotating, the DISG may be operated as a generator, providingregeneration, in place of, or in addition to, wheel braking as requestedby an operator through actuation of the brake pedal. In this way, theDISG replaces the driveline braking that would have been present if theengine was rotating. The DISG re-charges the battery or supplieselectrical power to accessory devices depending on the battery SOC. Thenwhen the operator requests additional output by pressing the acceleratorpedal, the engine may be restarted to supplement and/or replace the DISGoutput torque. Such transitions include crossing through thetransmission gear lash region (e.g., in the transmission or thetransmission final drive unit, and/or in the transmission reardifferential). Specifically, as noted previously herein, when theoperator presses the accelerator pedal during driveline braking,positive DISG and engine torque are applied to the driveline and thedriveline experiences a torque reversal (e.g. a negative to positivetorque transition). The torque reversal causes the driveline to crossthe lash zone (e.g. the tooth to tooth gear spacing in the reardifferential).

At time T₈₁, the brake pedal is released by the driver and the TCCcapacity is reduced as indicated by the TCC capacity trace beingreduced. Further, the DISG negative torque is reduced toward zero torquein response to less driveline braking is being called for as a result ofthe brake pedal being released. The transmission input shaft torque alsodecreases in response to DISG torque decreasing.

At time T₈₂, the driver depresses the accelerator pedal, therebyrequesting an increase in driveline positive torque. Shortly thereafter,the DISG torque changes from negative to positive and the TCC capacityis reduced by increasing TCC slip. The driveline disconnect clutch alsobegins to close in response to the increase in accelerator pedalposition. Closing the driveline disconnect clutch begins to acceleratethe engine. The transmission input shaft torque is gradually reducedfrom a small negative torque toward zero torque. Between time T₈₂ andtime T₈₃, the TCC capacity is reduced in response to an increase in adifference between a speed of a first gear tooth and a second geartooth. The speed difference between gear teeth results from thedriveline torque reversal.

At time T₈₃, the gear tooth to gear tooth speed difference between gearsis at its greatest level and then begins to decrease as the gear lash isreduced. The TCC capacity is increased in response to the gear toothspeed difference between gears decreasing. The DISG torque is alsoincreased in response to the speed difference between gear teethdecreasing so that the lash may be reduced. The driveline disconnectclutch state continues to increase indicating that an amount of torquethe driveline disconnect clutch is capable of transferring isincreasing. The accelerator pedal position and vehicle speed alsocontinue to increase.

At time T₈₄, the engine speed reaches the torque converter impellerspeed (same as DISG speed). The TCC capacity and driveline disconnectclutch are also increased in response to the engine speed reaching thetorque converter impeller speed. By waiting until engine speed equalstorque converter impeller speed to completely close the drivelinedisconnect clutch, it may be possible to reduce torque disturbances inthe driveline. The torque at the transmission input shaft transitionsfrom a negative torque to a positive torque in response to the drivelinetorque increasing. The DISG torque is also increased at a time after thetransmission input shaft torque transitions to a positive torque inresponse to the driveline disconnect clutch fully closing.

The example approach of this sequence recognizes several seeminglyunrelated piece of information, including (1) the engine and DISG torqueare additive when the driveline disconnect clutch 236 is closed; (2) dueto packaging constraints, especially associated with limits on thepowertrain length and diameter, the torque capacity of the DISG tends tobe significantly lower than the maximum engine torque; (3) DISG torqueis a function of DISG speed which is equal to the engine speed when theclutch is fully closed; and (4) the DISG torque is relatively constantup to a threshold rotor speed of approximately 1,000±100 RPM, and thenthe DISG torque is inversely proportional to DISG speed, referred to asthe constant power region, until frictional, eddy current and otherlosses cause the torque to decrease more rapidly with increasing rotorspeed at higher threshold speed (e.g., about 3,000+−500 RPM).

Thus, if the powertrain is operating in a regenerative braking mode,during a closed pedal event (e.g., the accelerator is not applied) withthe engine off, and then the operator presses the accelerator pedal. Theengine may remain off if the DISG is capable of delivering the desiredtorque. Then, the driveline disconnect clutch may remain open and theDISG can be quickly transitioned to near zero torque. The DISG operatesin a speed control mode and transitions slowly through the gear lashzone. The DISG quickly increases torque output after transitioningthrough the gear lash region to provide the desired torque. In this way,audible noise and torque impulses through a driveline may be reducedduring a driveline torque transition from negative torque to positivetorque.

Thus, the methods and systems of FIGS. 1-3 and 35-36 provide foroperating a driveline, comprising: stopping rotation of an engine andproviding regenerative braking via a driveline; transitioning from theregenerative braking to providing positive torque to the driveline; andoperating a driveline integrated starter/generator in a speed controlmode during the transition. The method includes where the drivelineintegrated starter/generator is operated in a torque control mode beforeand after operating the driveline integrated starter/generator in thespeed control mode. The method includes where the driveline integratedstarter/generator is adjusted to a speed based on a speed of a torqueconverter turbine.

In one example, the method further comprises opening a drivelinedisconnect clutch when the engine is stopped. The method furthercomprises closing a driveline disconnect clutch to start the engineafter operating the driveline integrated starter/generator in the speedcontrol mode. The method includes where the regenerative braking isprovided when a state of charge of an energy storage device is less thana threshold charge. The method further comprises increasing slip of atorque converter clutch during the transitioning from the regenerativebraking to providing positive torque to the driveline.

The methods and systems of FIGS. 1-3 and 35-36 provide for operating adriveline, comprising: stopping rotation of an engine and providingregenerative braking via a driveline integrated starter/generator;transitioning the driveline integrated starter/generator from providingthe regenerative braking to providing positive torque to the driveline;and adjusting slip of a torque converter clutch in response to thetransition from providing regenerative braking to providing positivetorque to the driveline. The further comprises operating the drivelineintegrated starter/generator in a speed control mode duringtransitioning the driveline integrated starter/generator from providingthe regenerative braking to providing positive torque to the driveline.

In one example, the method includes where the driveline integratedstarter/generator is operated at a speed that is a predetermined speedgreater than a torque converter turbine speed. The method furthercomprises increasing the speed in response to a reduction in gear lash.The method includes where adjusting slip of the torque converterincludes increasing torque converter slip. The method includes wheretransitioning the driveline integrated starter/generator from providingthe regenerative braking to providing positive torque to the drivelineis in response to an increasing torque demand. The method furthercomprises starting the engine via closing a driveline disconnect clutchwhile adjusting slip of the torque converter clutch.

The methods and systems of FIGS. 1-3 and 35-36 also provide for avehicle system, comprising: an engine; an electric machine; a drivelinedisconnect clutch positioned in a driveline between the engine and theelectric machine; a transmission; a torque converter positioned in thedriveline between the electric machine and the transmission; and acontroller including executable instructions stored in non-transitorymemory for reducing gear lash in the transmission via operating theelectric machine in a speed control mode and adjusting a speed of theelectric machine. The vehicle system further comprises a torqueconverter clutch and additional executable instructions to slip thetorque converter clutch when the electric machine is operated in thespeed control mode.

In some examples, the vehicle system further comprises additionalexecutable instructions to operate the electric machine at apredetermined speed that is greater than a speed of a turbine of thetorque converter. The vehicle system further comprises additionalexecutable instructions to increase a speed of the electric machineafter operating the electric machine at the predetermined speed. Thevehicle system further comprises additional executable instructions toprovide driveline brake torque via the electric machine. The vehiclesystem further comprises additional executable instructions to reducedriveline brake torque toward zero torque before operating the electricmachine in the speed control mode.

Referring now to FIG. 37, an example method for entering a sailing modeof driveline operation is shown. The method of FIG. 37 may be stored asexecutable instructions in non-transitory memory of controller 12 inFIGS. 1-3.

In one example, sailing mode may be characterized as combusting anair-fuel mixture in the engine while the driveline disconnect clutch isopen so that the engine provides substantially no torque (e.g., lessthan ±5 N-m) to the DISG, torque converter, and transmission. Sailingmode may include a sailing idle speed that is a lower speed than a baseidle speed that the engine operates at if the engine is coupled to thedriveline via a closed driveline disconnect clutch. The idle speed insailing mode is lower so that fuel may be conserved while in sailingmode. Further, spark timing in sailing mode may be more advanced thanspark timing when the engine is operating at based idle speed and thedriveline disconnect clutch is closed. Base idle speed may be describedas engine idle speed when the engine is warm and no accessory loads areapplied to the engine and when the engine is coupled to the DISG via thedriveline disconnect clutch. The engine may be operated at a lowerengine speed and with more spark advance in sailing mode than duringconditions where base idle speed is used because less reserve torque tocounteract transient loads that may be applied to the driveline may benecessary.

At 3702, method 3700 determines operating conditions. Operatingconditions may include but are not limited to driveline torque demand,driveline disconnect clutch state, engine speed, vehicle speed, DISGtorque, and battery state of charge. Method 3700 proceeds to 3704 afteroperating conditions are determined.

At 3704, method 3700 judges whether or not desired driveline torque isgreater than a threshold amount of torque that may be provided to thedriveline via the DISG. The threshold amount of torque may be slightlyless (e.g., 10% less) than rated DISG torque. In one example, anavailable DISG torque amount may estimated from empirically determinedvalues stored in a table that is indexed by DISG speed and DISGtemperature. The table outputs a maximum or available amount of torquethat may be provided to the driveline by the DISG. In other examples,the available or threshold DISG torque is less than the maximum DISGtorque so that the engine may be held in the sailing mode in case thedesired driveline torque approaches the maximum DISG torque. Further,the threshold DISG torque may increase or decrease in response tooperating conditions such as DISG temperature. Method 3700 comparesoutput from the table to the desired driveline torque amount. If method3700 judges that desired driveline torque is greater than the thresholdDISG torque, the answer is yes and method 3700 proceeds to 3706.Otherwise, the answer is no and method 3700 proceeds to 3716.

At 3706, method 3700 closes a driveline disconnect clutch to rotate andstart the engine. The driveline disconnect clutch may be closedaccording to a predetermined closing trajectory that is stored inmemory. Alternatively, the engine may be started via a starter otherthan the DISG and the driveline disconnect clutch is closed after theengine is accelerated to the speed of the DISG. The torque converterclutch slip may also be increased so as to reduce driveline torquedisturbances in response to desired torque. Method 3700 proceeds to 3708after the driveline disconnect clutch begins closing.

At 3708, method 3700 supplies fuel to the engine and the engine isstarted if it is not combusting an air-fuel mixture. Fuel and spark areprovided to engine cylinders to facilitate combustion within the engine.Method 3700 proceeds to 3710 after engine rotation begins.

At 3710, method 3700 judges whether or not energy storage device (e.g.,battery) state of charge is greater than a threshold amount. In oneexample, battery state of charge may be estimated from battery voltage.If method 3700 judges that battery state of charge is greater than athreshold amount, the answer is yes and method 3700 proceeds to 3714.Otherwise, the answer is no and method 3700 proceeds to 3712.

At 3714, method 3700 operates the engine and DISG to provide the desiredamount of driveline torque. The fraction of torque provided by each ofthe engine and the DISG may vary depending on operating conditions. Forexample, if battery state of charge is low, a greater portion ofdriveline torque may be provided by the engine rather than the DISG. Theamount of torque provided to the driveline by the engine may beestimated according to the method described in U.S. Pat. No. 7,066,121which is hereby fully incorporated for all intents and purposes. Theamount of torque provided to the driveline by the DISG may be estimatedfrom an empirically determined table that is indexed via DISG currentand speed. Method 3700 proceeds to exit after torque is provided to thedriveline via the engine and the DISG.

At 3712, method 3700 operates the engine without operating the DISG toprovide the desired torque to the driveline. Further, in some examples,the DISG may be transitioned to a battery charging mode where mechanicalenergy from the engine is converted into electrical energy via the DISGand stored in an electric energy storage device. In one example, engineair amount and engine fuel amount are adjusted to provide the desiredamount of driveline torque. For example, if the desired amount ofdriveline torque is increased, the amount of air and fuel supplied toengine cylinders is increased. Method 3700 proceeds to exit after engineoperation is adjusted to supply a desired amount of torque to thedriveline.

At 3716, method 3700 judges whether or not the engine is running andcombusting air-fuel mixtures in the engine cylinders. In one example,the engine may be determined to be combusting air-fuel mixtures whenengine torque increases as may be evidenced by increasing engine speed.If method 3700 judges that the engine is combusting air-fuel mixturesand running, the answer is yes and method 3700 proceeds to 3730.Otherwise, the answer is no and method 3700 proceeds to 3718.

At 3718, method 3700 judges whether or not battery state of charge isgreater than a threshold amount. In one example, battery voltage is abasis for estimating battery state of charge. If method 3700 judges thatbattery state of charge is greater than a threshold amount, the answeris yes and method 3700 proceeds to 3724. Otherwise, the answer is no andmethod 3700 proceeds to 3720.

At 3724, method 3700 provides the desired driveline torque via the DISGand without torque from the engine. Current is supplied to the DISGbased on a table stored in memory that outputs a DISG current amountbased on a desired DISG torque and DISG temperature. Values in the tablemay be empirically determined. Method 3700 proceeds to exit after theDISG torque is provided to the driveline.

At 3720, method 3700 rotates and starts the engine. The engine may berotated via a starter motor other than the DISG or by the DISG. If theengine is rotated by the DISG, the driveline disconnect clutch is closedto transfer torque from the DISG to the engine. The engine is started bysupplying fuel and spark to engine cylinders after the engine reachescranking speed. Engine cranking speed may be varied for differentoperating conditions. For example, if the engine is rotated by thestarter motor other than the DISG, the cranking speed is a speed lessthan 250 RPM. However, if the engine is rotated by the DISG, thecranking speed may be a speed less than 1200 RPM. Method 3700 proceedsto 3722 after the engine is rotated and started.

At 3722, method 3700 begins supplying at least a portion of enginetorque to vehicle wheels and begins charging the battery to increase thebattery state of charge. The driveline disconnect clutch is closed whenthe engine is providing torque to vehicle wheels and charging thebattery. Further, engine torque output is adjusted to provide thedesired driveline torque amount. The engine torque output may beincreased or decreased by adjusting cylinder air amount and cylinderfuel amount. Method 3700 proceeds to exit after at least a portion ofengine output is supplied to vehicle wheels.

At 3730, method 3700 judges whether or not selected conditions to entersailing mode are present. In one example, sailing mode may be enteredwhen engine temperature is greater than a threshold temperature.Further, other operating conditions such as engine speed and requestedtorque may be evaluated to determine if sailing mode may be entered.Additionally, in some examples, sailing mode may be entered when batterystate of charge is less than a threshold state of charge.

For example, sailing mode may also be entered when the catalysttemperature is below a threshold and other conditions. The controllermay selects to keep the engine at idle instead of turning off the enginebecause the emissions may increase if the engine is started with coolcatalysts. The controller may select to keep the engine at idle insteadof closing the driveline disconnect clutch and operating the engine toproduce torque if battery SOC is high and/or the current operating pointwould be required to have the engine operate at a low fuel efficientpoint.

Sailing mode may also be entered when the fuel vapor canister requirespurging. The controller may select to keep the engine at idle instead ofturning off the engine because fuel vapor purge is scheduled to run. Thecontroller may also select to keep the engine at idle instead of closingthe driveline disconnect clutch and operating the engine to producetorque if battery SOC is high and/or the current operating point wouldbe required to have the engine operate at a low fuel efficient point.

Sailing mode may also be entered when an increase in brake boost vacuumis desired. The controller may select to keep the engine at idle insteadof turning off the engine because vacuum is desired, and the engine isoperated to provide vacuum.

Sailing mode may be entered when engine coolant temperature (ECT) islow. The controller may select to keep the engine at idle instead ofturning off the engine because ECT is low.

Sailing mode may be entered when faster tip-in response for sport drivermode is desired. The controller may select to keep the engine at idleinstead of turning off the engine because the driving mode has beendetermined or selected as a sport mode. The response to driveraccelerator tip-ins will be faster with the engine at sailing idleinstead of if the engine is stopped.

If method 3700 judges that selected conditions are present to allowentry into sailing mode, the answer is yes and method 3700 proceeds to3732. Otherwise, the answer is no and method 3700 proceeds to 3718.

At 3732, method 3700 opens the driveline disconnect clutch. Thedriveline disconnect clutch is opened so that any torque produced by theengine is not supplied to the remaining portion of the drivelineincluding the DISG, the torque converter, and the transmission. Openingthe driveline disconnect clutch allows the engine to be operated at amore efficient operating state than if the engine were coupled to theDISG, torque converter, and transmission since the engine may beoperated with a smaller torque reserve. In one example, an engine torquereserve may be characterized as an amount of torque that is availablefrom the engine when the engine is operating at a particular speed andair amount without providing the total amount of available enginetorque.

For example, an engine may be producing 100 N-m of torque at 1200 RPMand at a prescribed cylinder air amount. However, the amount of enginetorque available at 1200 RPM when the engine is inducting the prescribedcylinder air amount may be 125 N-m. The difference of 25 N-m may beexplained by the engine operating at a spark timing that is retardedfrom MBT spark timing. The 25 N-m represents a torque reserve that maybe held to compensate for torque disturbances that may be supplied tothe engine. However, the 25 N-m also represents a loss of engineefficiency due to spark retard. The engine may be operated with asmaller torque reserve when the driveline disconnect clutch is opensince fewer torque disturbances may be applied to the engine via thedriveline. Method 3700 proceeds to 3734 after the driveline disconnectclutch is opened.

At 3734, method 3700 judges whether or not the desired driveline torqueis within a threshold range of a DISG torque threshold. The DISG torquethreshold may represent a maximum amount of torque available from theDISG or an amount of torque that is less than the total amount ofavailable DISG torque. If method 3700 judges that the desired drivelinetorque is within a threshold torque range of the DISG torque threshold,the answer is yes and method 3700 proceeds to 3736. Otherwise, theanswer is no and method 3700 proceeds to 3738.

At 3736, method 3700 operates the engine at a sailing idle speed andadjusts engine spark timing and valve timing to improve engineefficiency and fuel economy. The desired driveline torque is provided bythe DISG when the driveline disconnect clutch is in an open state. Thesailing idle speed may be lower than a based idle speed when the engineis coupled to the DISG and transmission. Further, spark timing while theengine is operated at sailing idle speed may be advanced as compared towhen the engine is operated at base idle speed. Base idle speed may beapplied when desired driveline torque is low and when the engine iscoupled to the remaining portion of the driveline via a closed drivelinedisconnect clutch. Engine valve timing can be adjusted to operate theengine at an improved volumetric efficiency. In one example, valvetiming is adjusted such that intake valve timing closes late to increaseengine intake manifold pressure while cylinder air charge is relativelylow. Method 3700 proceeds to exit after the engine enters sailing modeat 3736.

At 3738, method 3700 judges whether or not a starter other than the DISGis present in the system. In some examples, method 3700 may judge that astarter other than the DISG is not present if the starter other than theDISG is degraded. Method 3700 may also judges that a starter other thanthe DISG is present when a starter present bit is set in memory. Ifmethod 3700 judges that a starter other than the DISG is present, theanswer is yes and method 3700 proceeds to 3740. Otherwise, the answer isno and method 3700 proceeds to 3740.

At 3740, method 3700 stops engine rotation and the desired drivelinetorque is provided via the DISG. Engine rotation is stopped by stoppingfuel flow and spark to engine cylinders. The engine is stopped at 3740so that additional fuel may be conserved and because the engine may berestarted without torque from the DISG. In this way, a greater amount ofDISG torque may be supplied to the driveline because a portion ofavailable DISG torque does not have to be held in reserve to restart theengine. Method 3700 proceeds to exit after the engine is stopped.

At 3742, method 3700 judges whether or not DISG output torque is withina threshold range of engine cranking torque (e.g., an amount of torqueto rotate the engine from zero speed to a cranking speed of less than250 RPM). For example, if engine cranking torque is 40 N-m and athreshold range is 5 N-m, the DISG is within the threshold range ofengine cranking torque when the DISG output torque is 35.5 N-m. Ifmethod 3700 judges DISG output torque is within a threshold torque rangeof engine cranking torque, the answer is yes and method 3700 proceeds to3744. Otherwise, the answer is no and method 3700 proceeds to 3746.

At 3746, method 3700 stops engine rotation and provides the desireddriveline torque via the DISG. The engine is stopped to further reducefuel consumption. Since the DISG has a sufficient amount of torqueavailable to restart the engine, the engine may be stopped. If thedesired driveline torque increases while the engine is stopped, theengine may be restarted via the DISG before the DISG does not haveenough torque output capacity to start the engine and provide the desiredriveline torque. However, in some examples, the engine may continue toidle at sailing mode idle speed if battery state of charge is less thana threshold and the vehicle requires additional vacuum, fuel vaporpurging, higher catalyst temperature, or higher engine temperature.Method 3700 proceeds to exit after the engine is stopped.

At 3744, method 3700 operates the engine at sailing idle speed, adjustsspark timing, valve timing, and provides driveline torque via the DISGas described at 3736. Method 3700 proceeds to exit after the engineenters sailing mode.

It should be noted that when a driver reduces a driver demand torque(e.g., tips-out or reduces an accelerator input) the driveline mayoperate as follows according to the method of FIG. 37. Torque may beprovided from an engine to a driveline coupled to vehicle wheels whendriver demand torque is greater than a DISG threshold torque. The enginespeed may be reduced to a sailing mode idle speed and the enginedecoupled from the driveline in response to a decreasing driver demandtorque. The DISG may enter a regeneration mode providing charge to abattery and a constant deceleration rate for the vehicle. In oneexample, the DISG threshold torque is greater than 75% of a rated DISGtorque.

It should be noted that when a driver increases a driver demand torque(e.g., tips-in or increases an accelerator input) the driveline mayoperate as follows according to the method of FIG. 37. The engine mayaccelerate from a sailing idle speed to DISG speed in response to anincreasing driver demand torque. The driveline disconnect clutch may beclosed in response to the engine speed reaching the DISG speed.

It should be noted that when a driver increases a driver demand torque(e.g., tips-in or increases an accelerator input) during vehicle launchthe driveline may operate as follows according to the method of FIG. 37.DISG torque is provided to the vehicle driveline while the engine is notrotating in response to a driver demand torque. The engine may bestarted and idled at a sailing mode idle speed without providing enginetorque to the driveline in response to the driver demand torque beingwithin a threshold range of an engine cranking torque (e.g., where DISGtorque is greater than 75% of engine cranking torque). The engine may beaccelerated in a speed control mode to substantially match DISG speed(e.g., ±50 RPM) and the driveline disconnect clutch may be closed whenengine speed substantially matches DISG speed (e.g., ±50 RPM). In someexamples, engine speed may follow DISG speed when desired torque isbetween engine cranking torque and a threshold DISG torque (e.g., atorque between 75% of rated DISG torque and rated DISG torque).

Further, at 3736 and 3744 the engine may be operated in a speed controlmode to follow DISG speed when desired driveline torque is within apredetermined torque range of the DISG threshold torque. By followingthe DISG speed, the driveline disconnect clutch may be closed sooner soas to improve driveline response.

In this way, the method of FIG. 37 provides an efficient engineoperating mode that may reduce engine fuel consumption as compared tothe engine operating at base idle speed. Further, the method of FIG. 37provides for stopping the engine when additional fuel may be conserved.Additionally, the method maintains driveline torque response even thoughthe engine may be operated more efficiently or stopped.

Referring now to FIG. 38, an example method for exiting a sailing modeof driveline operation is shown. The method of FIG. 38 may be stored asexecutable instructions in non-transitory memory of controller 12 inFIGS. 1-3.

At 3802, method 3800 determines operating conditions. Operatingconditions may include but are not limited to driveline torque demand,driveline disconnect clutch state, engine speed, vehicle speed, DISGtorque, and battery state of charge. Method 3800 proceeds to 3804 afteroperating conditions are determined.

At 3804, method 3800 judges whether or not the engine in sailing mode ata sailing idle speed and if the driveline disconnect clutch is open. Theengine operating mode and driveline disconnect clutch operating statemay be determined via making an inquiry of one or more bits or flagsstored in memory. If method 3800 judges that the engine is not insailing mode, the answer is no and method 3800 proceeds to exit. Ifmethod 3800 judges that the engine is in sailing mode and the drivelinedisconnect clutch is open, the answer is yes and method 3800 proceeds to3806.

At 3806, method 3800 judges whether or not a desired driveline torque isgreater than a DISG threshold torque. The DISG threshold torque may beequal to or less than the available amount of DISG torque. If method3800 judges that the desired driveline torque is greater than the DISGthreshold torque, the answer is yes and method 3800 proceeds to 3808.Otherwise, the answer is no and method 3800 proceeds to exit.

At 3808, method 3800 increases engine speed from sailing idle speed to aspeed synchronous with DISG speed via increasing engine air amount andengine fuel amount (e.g., the amounts of air and fuel delivered toengine cylinders). Further, spark timing may be retarded away from MBTspark timing as the engine air amount and fuel amount are increased.Method 3800 proceeds to 3810 after engine air amount and fuel amount isincreased so that engine torque is increased and so that the engineaccelerated to the speed of the DISG.

At 3810, method 3800 increases an amount of torque converter clutch(TCC) slip. The torque converter clutch slip may be increased viadecreasing torque converter clutch application force. By increasing TCCslip, driveline torque disturbances may be reduced. Method 3800 proceedsto 3812 after TCC slip is increased.

At 3812, method 3800 closes the driveline disconnect clutch. Thedriveline disconnect clutch may be closed when the engine speed reachesthe DISG speed and after the engine speed has settled to the DISG speedfor a predetermined amount of time. Method 3800 proceeds to 3814 afterthe driveline disconnect clutch is closed.

At 3814, method 3800 increases engine torque via increasing the engineair and fuel amounts. Additionally, the DISG torque may be increased toaugment engine torque so that the desired driveline torque may beprovided. Method 3800 proceeds to exit after engine torque and DISGtorque are adjusted to provide the desired driveline torque.

In this way, the method of FIG. 38 provides for transitioning out ofsailing mode in response to a tip-in (e.g., depression of an acceleratorpedal to a higher torque demand) where the DISG is providing the torqueto the wheels and the engine is at idle. For example, the driver tips-inand the new torque demand increases quickly to above the total torquecapacity of the DISG. The engine accelerates in speed control modetowards the DISG speed, the TCC may be opened to allow torquemultiplication and isolation of the driveline and the drivelinedisconnect clutch may be closed to bring the engine up to speed veryquickly. The engine transitions to torque control after the enginesubstantially reaches DISG speed (e.g., +100 RPM). Subsequently, theengine and the DISG may provide the desired torque.

Referring now to FIG. 39, an example sequence for operating a drivelinethat includes a sailing mode according to the methods of FIGS. 37 and 38is shown. The sequence of FIG. 39 may be provided by the system of FIGS.1-3.

The first plot from the top of FIG. 39 represents vehicle speed versustime. The Y axis represents vehicle speed and vehicle speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The second plot from the top of FIG. 39 represents desired drivelinetorque versus time. The desired driveline torque may be a torque atvehicle wheels, a torque converter impeller, a torque converter turbine,or at a driveline disconnect clutch. The Y axis represents desireddriveline torque and desired driveline torque increases in the directionof the Y axis arrow. The X axis represents time and time increases fromthe left hand side of the figure to the right hand side of the figure.Horizontal line 3902 represents a threshold (e.g., a torque within aprescribed torque of rated or maximum DISG torque) driveline torque thata DISG has the capability to provide to the driveline. Horizontal line3904 represents a threshold (e.g., a torque within a prescribed torqueof engine cranking torque) amount of torque the DISG may provide whilehaving the capacity to crank the engine at cranking speed (e.g., 250RPM).

The third plot from the top of FIG. 39 represents the drivelinedisconnect clutch state versus time. The Y axis represents drivelinedisconnect state and the driveline disconnect clutch is closed when thedriveline disconnect clutch state trace is at a higher level near the Yaxis arrow. The driveline disconnect clutch is open when the drivelinedisconnect clutch state is at a lower level near the X axis. The X axisrepresents time and time increases from the left hand side of the figureto the right hand side of the figure.

The fourth plot from the top of FIG. 39 represents engine state versustime. The Y axis represents engine state and the engine is rotating whenthe engine state trace is at a higher level near the Y axis arrow. Theengine is not rotating when the engine state trace is in near the Xaxis. The X axis represents time and time increases from the left handside of the figure to the right hand side of the figure.

The fifth plot from the top of FIG. 39 represents energy storage deviceor battery state of charge (SOC) versus time. The Y axis representsbattery SOC and battery SOC increases in the direction of the Y axisarrow. The X axis represents time and time increases from the left handside of the figure to the right hand side of the figure. Horizontal line3906 represents a threshold amount of battery charge that is desired. Anamount of charge above 3906 may be desired to reduce the possibility ofbattery degradation.

At time T₈₅, vehicle speed is zero, the engine is stopped, the drivelinedisconnect clutch is open, battery state of charge is at a middle levelthat is greater than the level at 3906. These conditions may berepresentative of conditions when a vehicle is parked or stopped at atraffic signal.

At time T₈₆, the desired driveline torque increases in response to anincreasing driver demand torque as determined from an accelerator pedal(not shown). The engine remains in an off state and the drivelinedisconnect clutch remains closed. Vehicle speed begins to increase as adriveline integrated starter/generator (DISG) (not shown) begins tosupply positive torque to the vehicle driveline. Battery SOC begins todecline as battery charge is used to propel the vehicle.

Between time T₈₆ and time T₈₇, the desired driveline torque exceedstorque level 3904 in response to drive demand torque. As a result, theengine is rotated and started; however, the driveline disconnect clutchremains open. The engine may be started via a starter other than theDISG. Vehicle speed continues to increase and battery SOC continues todecrease.

At time T₈₇, the desired driveline torque exceeds torque level 3902 inresponse to driver demand torque. Shortly thereafter, the drivelinedisconnect clutch is closed in response to driveline torque exceedingthreshold torque level 3902. By closing the driveline disconnect clutch,driveline torque may be increased via increasing engine torque. Closingthe driveline disconnect clutch couples the engine to the DISG and theremaining driveline. The engine remains running and engine torque isincreased so that the desired driveline torque may be provided by theDISG and the engine. The battery SOC continues to decrease as the DISGsupplies torque to the driveline.

At time T₈₈, the desired driveline torque decreases in response todriver input to a level below threshold torque level 3902, but itremains above threshold torque level 3904. Engine torque is reduced inresponse to the reduced desired driveline torque. Additionally, thedriveline disconnect clutch is opened so as to decouple the engine fromthe DISG and driveline. The engine remains combusting air and fuel. Theengine speed may be reduced to a sailing idle speed that is lower than abase idle speed that the engine rotates at when the engine is coupled tothe DISG. Additionally, engine spark timing may be advanced. Reducingengine speed and advancing spark timing may decrease fuel consumption.

At time T₈₉, the desired driveline torque is increased for a second timeby the driver to a level above threshold torque 3902. The drivelinedisconnect clutch is closed in response to driveline torque exceedingtorque threshold 3902. Engine torque is then increased and the desireddriveline torque is provided via the engine. The DISG enters a generatormode and the battery state of charge is increased via a portion ofengine torque. Vehicle speed increases as engine torque is provided tothe driveline.

At time T₉₀, the desired driveline torque decreases in response to areduced driver demand torque. The desired driveline torque decreases toa torque below threshold torque 3904. Consequently, the drivelinedisconnect clutch is opened and engine rotation is stopped in responseto the low desired driveline torque. In this way, vehicle fuelconsumption may be reduced. The DISG stays in generator mode andincrease battery charge as the vehicle decelerates.

At time T₉₁, desired driveline torque is increased in response to driverdemand torque. The desired driveline torque is increased to a levelbetween torque threshold 3902 and torque threshold 3904. Since thedesired driveline torque is near threshold torque 3902 the engine isrotated and started so that engine torque may be made available in areduced amount of time if the desired driveline torque increasesfurther. The vehicle speed is increased by supplying torque to the DISG.Battery state of charge begins to decrease as the DISG supplies torqueto the vehicle driveline.

At time T₉₂, the desired driveline torque is increased in response toincreasing driver demand torque. The desired driveline torque increasesto a level greater than threshold torque 3902. Shortly thereafter, thedriveline disconnect clutch is closed and engine torque is provide thedriveline. In this way, driveline torque may readily be increasedwithout having to wait for engine speed to reach a level where torquemay be provided to the driveline. The DISG is also transitioned togenerator mode and battery SOC is increased.

At time T₉₃, the desired driveline torque decreases in response todriver input to a level below threshold torque level 3902, but itremains above threshold torque level 3904. Engine torque is reduced inresponse to the reduced desired driveline torque. Further, the drivelinedisconnect clutch is opened so as to decouple the engine from the DISGand driveline. The engine remains combusting air and fuel. The enginespeed may be reduced to a sailing idle speed. Torque is provided to thedriveline via the DISG which transitions to a torque mode outputting apositive torque to the vehicle driveline.

At time T₉₄, battery SOC is reduced to level 3906 as the DISG continuesto consume charge. The driveline disconnect clutch is closed in responseto the battery SOC and the DISG is transitioned to a generator mode. Theengine supplies torque to the driveline and the DISG. Thus, thedriveline disconnect clutch may be opened and closed in response todesired driveline torque and battery SOC. Shortly after time T₉₄, thedesired driveline torque is increased to a level above torque threshold3902. Since the driveline disconnect clutch is already closed, itremains in that state.

At time T₉₅, the desired driveline torque decreases in response to areduced driver demand torque. The desired driveline torque decreases toa torque below threshold torque 3904. Accordingly, the drivelinedisconnect clutch is opened and engine rotation is stopped in responseto the low desired driveline torque. The DISG stays in generator modeand increase battery charge as the vehicle decelerates.

Referring now to FIG. 40, an example sequence for operating a drivelinethat includes a sailing mode according to the methods of FIGS. 37 and 38is shown. The sequence of FIG. 40 may be provided by the system of FIGS.1-3.

The first plot from the top of FIG. 40 represents driveline disconnectclutch state versus time. The Y axis represents driveline disconnectclutch state and the driveline disconnect clutch is closed when thedriveline disconnect clutch state trace is at a higher level near the Yaxis arrow. The X axis represents time and time increases from the lefthand side of the figure to the right hand side of the figure.

The second plot from the top of FIG. 40 represents engine speed versustime. The Y axis represents engine speed and engine speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure. Horizontal line 4002 represents a base engine idle speedwhen the engine is coupled to the DISG via the driveline disconnectclutch. Horizontal line 4004 represents a base engine sailing mode idlespeed when the engine is combusting air and fuel but is not coupled tothe DISG.

The third plot from the top of FIG. 40 represents DISG torque versustime. The Y axis represents DISG torque and DISG torque increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure. Horizontal line 4006 represents an amount of torque theDISG is capable of providing to the driveline (e.g., a rated DISGtorque). Horizontal line 4008 represents an amount of torque the DISG iscapable of providing to the driveline while being able to crank theengine from zero speed.

The fourth plot from the top of FIG. 40 represents desired drivelinetorque versus time. The Y axis represents desired driveline torque anddesired driveline torque increases in the direction of the Y axis arrow.In one example, the desired driveling torque is based on driver demandtorque as determined from an accelerator pedal. The X axis representstime and time increases from the left hand side of the figure to theright hand side of the figure.

The fifth plot from the top of FIG. 40 represents operating state of alow power starter (e.g., a starter with lower starting power than theDISG). The Y axis represents the operating state of the low powerstarter and the low power starter is rotating when the low power starterstate trace is near the Y axis arrow. The X axis represents time andtime increases from the left hand side of the figure to the right handside of the figure.

At time T₉₆, the driveline disconnect clutch is closed and the enginespeed is at an elevated level. The engine is providing positive torqueto the driveline. The DISG torque is at a low level indicating theengine is providing most of the torque to the driveline. Further, thelow capacity starter is not operating.

Between time T₉₆ and time T₉₇, the driveline disconnect clutch is openedand the engine is stopped in response to a reduction in the desireddriveline torque. The desired driveline torque decreases in response toa decrease in drive demand torque (not shown). The low capacity starterremains off and the DISG torque remains at a lower level.

At time T₉₇, the driveline disconnect clutch is partially closed inresponse to a low state of battery charge (not shown). The DISG torqueis briefly increased in response to closing the driveline disconnectclutch. The DISG provides additional torque to the driveline forstarting the engine. Shortly thereafter, the engine is started bysupplying fuel and spark to the engine. The DISG torque is decreasedafter the engine is started and DISG torque turns negative when the DISGenters a generator mode to charge the battery. The engine is crankedwithout the low capacity starter via the driveline disconnect clutch andthe DISG at a time when the DISG torque is below threshold 4008.

Between time T₉₇ and time T₉₈, the engine and DISG charges the battery.The engine is stopped after the battery is charged and the DISG beginsto provide positive torque to the driveline. The driveline disconnectclutch is also opened when the engine is stopped. The desired drivelinetorque is increased shortly after the engine is stopped in response toan increasing driver demand torque. However, the desired drivelinetorque is not within a threshold range of torque level 4006 so theengine is not started.

At time T₉₈, the desired driveline torque is increased to a level thatis within a threshold range of torque to torque level 4006. The lowcapacity starter is engaged and rotates the engine in response to theincrease in desired driveline torque. The engine starts shortlythereafter when spark and fuel are supplied to the engine. The drivelinedisconnect clutch remains in an open state since the DISG can providethe desired driveline torque without assistance from the engine. Theengine operates at the sailing idle speed in anticipation of anincreased desired driveline torque.

At time T₉₉, the desired driveline torque decreases to a level belowthreshold level 4008 in response to a reduced driver demand torque (notshown). The engine is stopped in response to the low desired drivelinetorque and the low capacity starter remains off. The drivelinedisconnect clutch also remains in an open state.

Between time T₉₉ and time T₁₀₀, the desired driveline torque isincreased in response to an increased driver demand torque. The desireddriveline torque is increased to a level that is less than a thresholdtorque away from the torque level 4006. Therefore, the DISG provides thedesired driveline torque without starting the engine. The drivelinedisconnect clutch remains in an open state.

At time T₁₀₀, the desired driveline torque is increased further inresponse to an increased driver demand torque. The low capacity starteris engaged and the engine is rotated in response to the desireddriveline torque increasing to within a threshold level of torque level4006. The engine is started by supplying spark and fuel to the engine isresponse to engine rotation. The engine is accelerated up to the sailingmode idle speed 4004. The DISG continues to supply all positive torqueto the driveline to meet the desired driveline torque. The low capacitystarter is disengaged shortly after the engine is started.

At time T₁₀₁, the desired driveline torque is increased to a levelgreater than torque level 4006 in response to an increasing driverdemand torque. The driveline disconnect clutch and is closed in responseto the increasing driver demand torque and engine speed is alsoincreased so that the engine may provide additional torque to augmentthe DISG torque. The low capacity starter remains off.

In this way, the starter, engine, and disconnect clutch may be operatedto provide shorter response time to an increase in desired drivelinetorque. Further, the low capacity starter may be operated duringconditions where the DISG lacks capacity to crank the engine so that theDISG operating range may be extended.

Thus, the methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: operating an engine andproviding engine torque to a driveline propelling a vehicle in responseto a desired torque being greater than a threshold driveline integratedstarter/generator torque; and operating the engine and not providingengine torque to the driveline in response to the desired torque beingless than the threshold driveline torque and greater than a thresholdengine cranking torque. In this way, a driveline may operate withimproved efficiency and provide a shorter torque response time.

In some examples, the method includes where the threshold drivelineintegrated starter/generator torque is a torque of within apredetermined torque range of a rated torque of a driveline integratedstarter/generator. The method includes where the threshold enginecranking torque is within a predetermined torque range of an enginecranking torque. The method includes where the engine cranking torque isa torque to rotate the engine from zero rotation to a speed less than250 RPM. The method further comprises operating a driveline disconnectclutch in an open state while operating the engine and not providingengine torque to the driveline. The method includes where the desiredtorque is based on a driver demand torque. The method further comprisesproviding torque to the driveline via a driveline integratedstarter/generator while operating the engine and not providing enginetorque to the driveline.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: rotating an engine and providingengine torque to a driveline propelling a vehicle in response to adesired torque being greater than a threshold driveline integratedstarter/generator torque; rotating the engine and not providing enginetorque to the driveline in response to the desired torque being lessthan the threshold driveline torque and greater than a threshold enginecranking torque; and not rotating the engine in response to the desiredtorque being less than the threshold engine cranking torque. The methodfurther comprises rotating and operating the engine in response to abattery state of charge when the desired torque is less than thethreshold engine cranking torque.

In one example, the method further comprises rotating the engine from astopped state in response to the desired torque being greater than thethreshold driveline integrated starter/generator torque. The methodincludes where the threshold driveline integrated starter/generatortorque is less than a predetermined torque away from a rated drivelineintegrated starter/generator torque. The method includes where adriveline disconnect clutch is in a closed state when providing enginetorque to the driveline propelling the vehicle. The method includeswhere a driveline disconnect clutch is in an open state when notproviding engine torque to the driveline propelling the vehicle. Themethod includes where a threshold driveline integrated starter/generatortorque varies with vehicle operating conditions.

The methods and systems of FIGS. 1-3 and 37-40 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller including executableinstructions stored in non-transitory memory to idle an engine at afirst idle speed while the driveline disconnect clutch is in an openstate, and executable instructions to idle the engine at a second idlespeed, the second idle speed greater than the first idle speed, whilethe driveline disconnect clutch is in a closed state.

In one example, the vehicle system further comprises additionalexecutable instructions for opening and closing the driveline disconnectclutch in response to a desired driveline torque. The vehicle systemfurther comprises additional executable instructions to advance sparktiming and reduce engine air amount in response to the engine operatingat the first idle speed. The vehicle system further comprises additionalexecutable instructions to retard spark timing and increase engine airamount relative to spark timing and engine air amount when the engineoperated at the first idle speed. The vehicle system further comprisesadditional executable instructions to provide engine torque to thetransmission in response to a desired torque being greater than athreshold driveline integrated starter/generator torque. The vehiclesystem further comprises additional executable instructions to notprovide engine torque to the transmission in response to the desiredtorque being less than a threshold driveline integratedstarter/generator torque.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: operating an engine at apredetermined sailing idle speed, the sailing idle speed less than abase engine idle speed; and opening a driveline disconnect clutch whilethe engine is operating at the predetermined sailing idle speed todecouple the engine from vehicle wheels. The method includes where theengine is operated at the predetermined sailing idle speed when adesired driveline torque is within a threshold range of a drivelineintegrated starter/generator (DISG) threshold torque and when the DISGis supplying torque to vehicle wheels and where vehicle is moving whilethe engine is at the predetermined sailing idle speed. The methodincludes where the DISG threshold torque is maximum torque capacity ofthe DISG.

In some examples, the method further comprises where spark timing ismore advanced than spark timing at base engine idle speed. The methodfurther comprising exiting sailing idle speed in response to a desiredtorque exceeds a threshold value. The method further comprises closingthe driveline disconnect clutch in response to the desired torqueexceeding the threshold value. The method includes where the drivelinedisconnect clutch is in a driveline positioned between the engine and adriveline integrated starter/generator.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: operating an engine at apredetermined sailing idle speed in response to an operating state wherea driveline integrated starter/generator (DISG) lacks torque to start anengine from rest, the sailing idle speed less than a base engine idlespeed; and opening a driveline disconnect clutch while the engine isoperating at the predetermined sailing idle speed to decouple the enginefrom vehicle wheels. The method further comprises providing a desireddriveline torque to vehicle wheels via a DISG while the engine isoperating at the predetermined sailing idle speed.

In one example, the method further comprises exiting operating theengine at the predetermined sailing idle speed in response to a torquerequest greater than a threshold value. The method includes where theengine is decoupled from the DISG. The method includes where the engineis decoupled from a transmission. The method further comprisesaccelerating the engine to a speed of the DISG before closing thedriveline disconnect clutch. The method includes where spark supplied tothe engine while the engine is operating at the predetermined sailingidle speed is more advance than when the engine is operated at a baseidle speed.

The methods and systems of FIGS. 1-3 and 37-40 also provide for avehicle system, comprising: an engine; a dual mass flywheel (DMF)including a first side mechanically coupled to the engine; a drivelinedisconnect clutch mechanically including a first side coupled to asecond side of the dual mass flywheel; a driveline integratedstarter/generator (DISG) including a first side coupled to a second sideof the driveline disconnect clutch; a transmission selectively coupledto the engine via the driveline disconnect clutch; and a controllerincluding non-transitory instructions executable to enter a sailing modein response to a desired torque.

In one example, the vehicle system further comprises additionalinstructions to enter sailing mode in response to the desired torqueoutput being within a threshold torque of a DISG torque capacity. Thevehicle system further comprises additional instructions to entersailing mode in response to insufficient available DISG torque to startthe engine. The vehicle system further comprises additional instructionsto exit sailing mode in response to the desired torque being greaterthan a threshold. The vehicle system further comprises additionalinstructions to increase engine speed in response to exiting sailingmode. The vehicle system further comprises additional instructions toclose the driveline disconnect clutch when engine speed is substantiallyat DISG speed.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: providing torque from an engineto a driveline coupled to wheels; operating the engine at an idle speedand decoupling the engine from the driveline in response to a reduceddriver demand torque; and providing a constant vehicle deceleration rateduring the reduced driver demand torque. In this way, a driveline mayconserve fuel while providing driveline braking and improving torqueresponse.

In some examples, the method further comprises opening a drivelinedisconnect clutch in response to the reduced driver demand torque. Themethod includes where a driveline integrated starter/generator providesa negative torque to provide the constant vehicle deceleration rate. Themethod includes where the idle speed is a first idle speed, and wherethe first idle speed is lower than a second idle speed, the engineoperated at the second idle speed when the engine is coupled to thedriveline. The method includes where the engine is operated at the idlespeed in response to the reduced driver demand torque being less than adriveline integrated starter/generator threshold torque. The methodincludes where the driveline integrated starter/generator thresholdtorque is greater than 75% of a rated driveline integratedstarter/generator torque. The method includes where the torque providedfrom the engine is a positive torque.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: providing torque from an engineto a driveline coupled to wheels; operating the engine at idle speed anddecoupling the engine from the driveline in response to a reduced driverdemand torque; providing a constant vehicle deceleration rate at thereduced driver demand torque; and accelerating the engine to a speed inresponse to an increase in driver demand torque after operating theengine at the idle speed. The method includes where the speed is adriveline integrated starter/generator speed.

In some examples, the method further comprises closing a drivelinedisconnect clutch in response to the speed reaching the drivelineintegrated starter/generator speed. The method includes where theconstant vehicle deceleration is provided via a driveline integratedstarter/generator. The method includes where the driveline integratedstarter/generator is operated in a regeneration mode charging a battery.The method includes where the idle speed is a first idle speed, andwhere the first idle speed is lower than a second idle speed, the engineoperated at the second idle speed when the engine is coupled to thedriveline. The method includes where the engine is operated at the idlespeed in response to the reduced driver demand torque being less than adriveline integrated starter/generator threshold torque.

The methods and systems of FIGS. 1-3 and 37-40 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller including executableinstructions stored in non-transitory memory to provide a constantvehicle deceleration rate while idling the engine at a sailing mode idlespeed.

In one example, the vehicle system includes where the sailing mode idlespeed is a speed less than a base idle speed, the base idle speedprovided when the engine is coupled to the DISG. The vehicle systemfurther comprises additional instructions to open the drivelinedisconnect clutch in response to a decreasing driver demand torque. Thevehicle system further comprises additional instructions to exit sailingmode idle speed in response to an increasing driver demand torque. Thevehicle system further comprises additional instructions to increaseengine speed from sailing mode idle speed in response to an increasingdriver demand torque. The vehicle system includes where the constantvehicle deceleration rate is provided via the DISG.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: providing torque to a drivelinevia a driveline integrated starter/generator in response to a desiredtorque; and starting an engine and idling the engine without providingengine torque to the driveline in response to the driver demand torquebeing within a threshold range of an engine cranking torque. In thisway, different levels of desired driveline torque may be the basis forentering or exiting sailing mode. The method includes where thethreshold range is greater than 75% of engine cranking torque. Themethod includes where the DISG torque is provided to a torque converter.The method includes where the engine is started via the drivelineintegrated starter/generator. The method includes where a drivelinedisconnect clutch is in an open state while idling the engine. Themethod also includes where the desired torque is based on a driverdemand torque. The method includes where the engine cranking torque isan amount of torque to accelerated the engine from zero speed to a speedless than 250 RPM.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: providing torque to a drivelinevia a driveline integrated starter/generator in response to a driverdemand torque; starting an engine and idling the engine withoutproviding engine torque to the driveline in response to the driverdemand torque being within a threshold range of an engine crankingtorque; and accelerating the engine to driveline integratedstarter/generator speed in response to the driver demand torqueincreasing to a threshold driveline integrated starter/generator torque.The method further comprises closing a driveline disconnect clutch inresponse to the engine reaching the driveline integratedstarter/generator speed.

In one example, the method further comprises providing engine torque tothe driveline after closing the driveline disconnect clutch. The methodincludes where the engine is started via a starter other than thedriveline integrated starter/generator. The method includes where theengine is started via the driveline integrated starter/generator. Themethod includes where the engine is idled at a sailing mode idle speed.The method includes where spark supplied to the engine while the engineis operating at the sailing mode idle speed is more advance than whenthe engine is operated at a base idle speed.

The methods and systems of FIGS. 1-3 and 37-40 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller including executableinstructions stored in non-transitory memory to accelerate a vehiclefrom zero speed via the DISG without starting the engine, andinstructions to start the engine in response to a desired torqueexceeding a threshold engine cranking torque.

In one example, the vehicle system further comprises additionalinstructions to idle the engine at a sailing idle speed withoutproviding engine torque to the driveline. The vehicle system furthercomprises additional instructions to accelerate the engine from thesailing idle speed in response to an increasing desired torque. Thevehicle system further comprises additional instructions to close thedriveline disconnect clutch in response to engine speed reaching DISGspeed. The vehicle system further comprises additional instructions toincrease engine torque after closing the driveline disconnect clutch.The vehicle system includes where the engine cranking torque is anamount of torque to accelerate the engine from zero rotational speed toan engine speed of less than 250 RPM.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: providing positive torque to adriveline via a driveline integrated starter/generator; operating anengine at an idle speed in a speed control mode; and accelerating theengine in the speed control mode to driveline integratedstarter/generator speed in response to a desired torque. In this way,torque converter torque may be controlled during a tip-in condition. Themethod includes where the desired torque is a driver demand torque, andwhere a driveline disconnect clutch positioned in the driveline betweenthe engine and the driveline integrated starter/generator is in an openstate.

In one example, the method further comprises closing the drivelinedisconnect clutch in response to engine speed reaching or exceedingdriveline integrated starter/generator speed. The method includes wherethe idle speed is a sailing mode idle speed. The method includes wherethe sailing mode idle speed is a lower speed than a base engine idlespeed. The method further comprises advancing engine spark timing whilethe engine operates in the sailing mode idle speed with respect toengine spark timing of the engine while operating the engine at the baseengine idle speed. The method further comprises reducing an engine airamount while the engine operates in the sailing mode idle speed withrespect to engine air amount while operating the engine at the baseengine idle speed.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: providing positive torque to adriveline via a driveline integrated starter/generator; operating anengine at an idle speed in a speed control mode; adjusting torqueconverter clutch slip and accelerating the engine in the speed controlmode to driveline integrated starter/generator speed in response to adesired torque; and closing a driveline disconnect clutch in response toengine speed substantially matching driveline integratedstarter/generator speed. The method includes where adjusting torqueconverter slip includes increasing torque converter slip. The methodfurther comprises reducing torque converter slip in response to thedriveline disconnect clutch being in a closed state.

In some examples, the method includes where the idle speed is a sailingmode idle speed. The method includes where the sailing mode idle speedis a lower speed than a base engine idle speed. The method includeswhere the desired torque is increasing. The method includes where thedesired torque increases to a torque greater than a threshold drivelineintegrated starter/generator torque.

The methods and systems of FIGS. 1-3 and 37-40 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller including executableinstructions stored in non-transitory memory to solely provide positivetorque to the transmission via the DISG in response to a desired torquebeing less than an engine cranking torque, and instructions adjustingengine speed to follow DISG speed when DISG torque is greater and theengine cranking torque and less than a threshold DISG torque.

In one example, the vehicle system further comprises additionalinstructions to close the driveline disconnect clutch when engine speedis substantially equal to DISG speed. The vehicle system furthercomprises additional instructions to operate the engine in a torquecontrol mode after closing the driveline disconnect clutch. The vehiclesystem further comprises additional instructions to operate the enginein a speed control mode while adjusting engine speed to follow DISGspeed. The vehicle system further comprises additional instructions toprovide the desired torque via the engine and the DISG. The vehiclesystem further comprises a torque converter and torque converter clutch,and further comprising additional instructions to increase torqueconverter clutch slip in response to the desired torque.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: providing torque to a drivelinecoupled to vehicle wheels via an engine and a driveline integratedstarter/generator (DISG); and entering a sailing mode during selectconditions, the sailing mode including providing DISG torque to thedriveline and idling the engine without providing engine torque to thedriveline. The method includes where the select conditions include wherea catalyst temperature is less than a threshold temperature. The methodincludes where the select conditions include where a fuel vapor canisterhas stored more than a threshold amount of fuel vapor. The methodincludes where the select conditions include where a vacuum level isless than a threshold vacuum. The method includes where the selectconditions include where an engine coolant temperature is less than athreshold temperature. The method includes where the select conditionsinclude where a driver has selected a sport driving mode. The methodincludes where the engine is idled at a sailing mode idle speed that isa lower idle speed than a base idle speed when the engine is coupled tothe DISG.

The methods and systems of FIGS. 1-3 and 37-40 also provide for adriveline operating method, comprising: providing torque to a drivelinecoupled to vehicle wheels via an engine and a driveline integratedstarter/generator (DISG); entering a sailing mode during selectconditions, the sailing mode including providing DISG torque to thedriveline and idling the engine without providing engine torque to thedriveline; and advancing spark timing and reducing engine air amount inresponse to entering the sailing mode. The method includes where theselect conditions include where a catalyst temperature is less than athreshold temperature and where an energy storage device state of chargeis equal to or greater than a threshold state of charge.

In some examples, the method includes where the select conditionsinclude where a fuel vapor canister has stored more than a thresholdamount of fuel vapor and where energy storage device state of charge isequal to or greater than a threshold state of charge. The methodincludes where the select conditions include where a vacuum level isless than a threshold vacuum and where an energy storage device state ofcharge is equal to or greater than a threshold state of charge. Themethod includes where the select conditions include where an enginecoolant temperature is less than a threshold temperature and where anenergy storage device state of charge is equal to or greater than athreshold state of charge. The method includes where the selectconditions include where a driver has selected a sport driving mode andwhere an energy storage device state of charge is equal to or greaterthan a threshold state of charge. The method includes where the engineis idled at a sailing mode idle speed that is a lower idle speed than abase idle speed when the engine is coupled to the DISG.

The methods and systems of FIGS. 1-3 and 37-40 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller including executableinstructions stored in non-transitory memory to enter a sailing modeduring select conditions, where the engine is operated at a sailing modeidle speed without providing engine torque to the transmission and whereDISG torque is provided to the transmission, where the select conditionsinclude battery state of charge being equal or greater than a thresholdbattery charge.

In one example, the vehicle system further comprises additionalinstructions to purge fuel vapors during the sailing mode. The vehiclesystem further comprises additional instructions to generate vacuumduring the sailing mode. The vehicle system further comprises additionalinstructions to increase catalyst temperature during the sailing mode.The vehicle system further comprises additional instructions to increaseengine temperature during the sailing mode. The vehicle system includeswhere the threshold battery charge is a rated battery charge.

Referring now to FIGS. 41 and 42, a flowchart of a method for adapting adriveline disconnect clutch transfer function is shown. The method ofFIGS. 41 and 42 may be stored as executable instructions innon-transitory memory of controller 12 in FIGS. 1-3.

At 4102, method 4100 judges whether or not conditions are present fordriveline disconnect clutch adaptation. Driveline disconnect clutchadaptation may be implemented starting with the driveline disconnectclutch in an open state and after the driveline disconnect clutchreaches a predetermined operating temperature and after the engine andDISG reach selected operating conditions, such as minimum engine andDISG operating temperatures. In still another example, drivelinedisconnect clutch adaptation may be provided during conditions wheretorque converter impeller speed is greater than torque converter turbinespeed. If method 4100 judges that conditions are present for drivelinedisconnect clutch adaptation, the answer is yes and method 4100 proceedsto 4104. Otherwise, the answer is no and method 4100 proceeds to exit.

At 4104, method 4100 opens the torque converter clutch (TCC) and theDISG is rotated if there is no torque sensor or if the engine is notrotating and combusting. If there is a torque sensor, torque measurementis not based on impeller speed. If the engine is rotating and combustingthe method of FIG. 42 does not require the DISG to be turning. When DISGrotation is required, the DISG rotates under its own power via currentsupplied by an energy storage device. In one example, the DISG isrotated at less than 1000 RPM so that very little torque is transferredthrough the torque converter to the transmission. Thus, the DISG may berotated at a speed that provides less than a threshold amount of torquethrough the torque converter to the transmission. Method 4100 proceedsto 4106 after the TCC is opened.

At 4106, method 4100 judges whether or not the engine is rotating andcombusting an air-fuel mixture. In one example, the engine may be judgedto be rotating and combusting an air fuel mixture when engine speed isgreater than a threshold speed. If method 4100 judges that the engine isrotating and combusting an air-fuel mixture, the answer is yes andmethod 4100 proceeds to 4150. Otherwise, the answer is no and method4100 proceeds to 4108.

At 4150, method 4100 operates the engine in a speed control mode.Further, the vehicle speed may be zero. The engine may be combusting anair-fuel mixture when driveline disconnect clutch adaptation begins orthe engine may be started via a starter or the DISG. The converterclutch is in an open state and engine speed is controlled via varyingengine torque by way of the engine throttle, spark timing, cam timing,valve lift, fuel injection or other actuators. Method 4100 proceeds to4152 after the engine is put in a speed control mode.

At 4152, method 4100 adjusts engine speed to be above or below DISGspeed. For example, if DISG speed is 400 RPM, engine speed may beadjusted to 800 RPM. Alternatively, engine speed can be adjusted to 700RPM if DISG speed is 800 RPM, for example. Method 4100 proceeds to 4154after engine speed is adjusted.

At 4154, method 4100 estimates engine torque and stores the estimatedengine torque in memory. Engine torque may be estimated as is describedin U.S. Pat. No. 7,066,121. Alternatively, engine torque may beestimated via other known methods. For example, engine torque may beempirically determined at selected engine speeds and engine loads. Theempirical data is stored in controller memory and retrieved via indexingtables or functions based on present engine speed and load. Method 4100proceeds to 4156 after engine torque is estimated.

At 4156, method 4100 incrementally increases the driveline disconnectclutch application pressure. In one example, the driveline disconnectclutch application pressure may be increased via increasing a duty cycleof a driveline disconnect clutch control signal. A higher duty cycleincreases oil pressure supplied to the driveline disconnect clutch. Theincremental increase in driveline disconnect application pressure may bepredetermined and stored in memory as a driveline disconnect clutchtransfer function. The driveline disconnect clutch transfer functionrelates driveline disconnect clutch application pressure and drivelinedisconnect clutch input torque and outputs a driveline disconnect clutchoutput torque. The driveline disconnect clutch transfer function mayalso be used to select a driveline disconnect clutch applicationpressure by indexing the transfer function via desired clutch outputtorque and clutch input torque.

The driveline disconnect clutch application pressure or force, enginespeed, and DISG speed are stored in memory each time the drivelinedisconnect clutch application pressure is increased. Each time thedisconnect clutch torque is changed to a new level (there may bemultiple levels used in sequence to learn the clutch transfer functionas per method 4130 and FIG. 43), the system needs may wait for enginespeed to stabilize at the desired engine speed and then a new estimateof engine torque is stored. Once the engine speed controller hasrejected any disturbance from the change in disconnect clutch torque,store both the estimated engine torque and the estimated disconnectclutch torque for use at 4160. The engine controller may use theestimated disconnect clutch pressure or capacity and the sign of theslip across the disconnect clutch to proactively increase or decreaseengine torque as appropriate, or the engine control may only usefeedback control to compensate engine speed for changes in disconnectclutch pressure. Method 4100 proceeds to 4158 after the drivelinedisconnect clutch application pressure is increased.

At 4158, method 4100 judges whether or not the driveline disconnectclutch application profile has been completely applied. In one example,the driveline disconnect clutch application profile provides only enoughpressure to transmit minimal torque (e.g. 2 Nm) for one clutch plate tojust begin to touch the other clutch plate. In other examples, thedriveline disconnect clutch application profile may transition fromfully open to fully closed. If method 4100 judges that not allapplication pressures of the driveline disconnect clutch profile havebeen applied, the answer is no and method 4100 returns to 4154.Otherwise, the answer is yes and method 4100 proceeds to 4160.

At 4160, method 4100 compares the driveline disconnect clutch torqueestimate(s) from the driveline disconnect clutch transfer function tothe engine torque estimate(s) stored when engine speed was stabilized atthe desired speed at each of the commanded disconnect clutch pressureswhen the driveline disconnect clutch transfer function is applied viaincrementing the driveline disconnect clutch application pressure. Forexample, if the driveline disconnect clutch transfer function outputs adriveline disconnect clutch duty cycle of 35% (corresponding to adesired driveline disconnect clutch application pressure or force) forachieving a desired disconnect clutch output torque of 50 N-m when thedriveline disconnect clutch input torque is 85 N-m, but the drivelinedisconnect clutch output torque is 45 N-m as estimated by the enginetorque estimator, it may be judged that the driveline disconnect clutchtransfer function has an error of 5 N-m when the 35% duty cycle isapplied to the driveline disconnect clutch when the driveline disconnectclutch input torque is 85 N-m. The difference between the desireddriveline disconnect clutch torque and the engine torque may bedetermined for each set of operating conditions where the drivelinedisconnect clutch transfer function was applied at 4156. Method 4100proceeds to 4162 after the driveline disconnect clutch torque as definedby the driveline disconnect clutch transfer function is compared to thetorque estimated by the engine when the driveline disconnect clutchapplication pressure is incremented.

At 4162, method 4100 updates the driveline disconnect clutch transferfunction at selected entries in response to error between drivelinedisconnect clutch torque estimated by the engine and drivelinedisconnect clutch torque expected based on the driveline disconnectclutch transfer function. In one example, if the driveline disconnectclutch torque estimated by the engine differs from the drivelinedisconnect clutch torque estimated from the driveline disconnect clutchtransfer function, the driveline disconnect clutch torque estimated bythe engine replaces the corresponding driveline disconnect clutch torquevalue in the driveline disconnect clutch transfer function. In this way,the engine torque estimator may be the basis for adjusting the drivelinedisconnect clutch transfer function. Method 4100 proceeds to 4164 afterthe disconnect transfer function is updated at selected values wheredriveline disconnect clutch torque estimated by the engine disagreeswith driveline disconnect clutch torque described in the drivelinedisconnect clutch transfer function.

If the difference between the engine torque based estimated disconnectclutch torque and the previous disconnect clutch torque is above athreshold, the adaptation sequence may be rerun to test the system againat the next opportunity and the adaptation sequence may be executeduntil the system is successfully adapted. It should be noted that alladaptation methods described herein may be executed more frequently,sooner, or immediately in response to a magnitude in error of thedriveline disconnect clutch transfer function.

At 4164, method 4100 applies the revised driveline disconnect clutchtransfer function to scheduled driveline disconnect clutch pressure. Forexample, when an adjustment to driveline disconnect clutch pressure isrequested, the driveline disconnect clutch pressure is output based onthe revised driveline disconnect clutch transfer function at 4162.Method 4100 exits after the revised driveline disconnect clutchpressures are output.

At 4108, method 4100 judges whether or not an engine restart isrequested. If engine rotation is stopped at 4108 it may be restarted ifdesired. If an engine restart is requested during driveline disconnectclutch adaptation, it may be possible that errors may be present in theadapted driveline disconnect clutch transfer function. Therefore,driveline disconnect clutch adaption is not performed during enginerestarts. If method 4100 determines that an engine restart is desired,the answer is yes and method 4100 proceeds to exit. Otherwise, theanswer is no and method 4100 proceeds to 4110.

At 4110, method 4100 judges whether or not a driveline torque sensor ispresent to detect driveline torque. If method 4100 judges that adriveline torque sensor is present, the answer is yes and method 4100proceeds to 4130. Otherwise, the answer is no and method 4100 proceedsto 4112.

Note that in some examples, driveline disconnect clutch adaptation basedon the torque converter (e.g., 4112-4122) or the torque sensor (e.g.,4130-4138) may be conducted simultaneously with the engine torque basedestimate of driveline disconnect clutch torque (e.g., 4150-4164) if theengine and DISG speeds are kept separate (e.g., the driveline disconnectclutch slips) and the engine controller is operated in closed loopengine speed control.

At 4130, method 4100 increases driveline disconnect clutch pressure froma state where the driveline disconnect clutch is in a fully open stateby sequentially increasing driveline disconnect clutch applicationpressure. The driveline disconnect clutch pressure may be increased at apredetermined rate or according to a predetermined group of selecteddriveline disconnect clutch application pressure increments. Method 4100proceeds to 4132 after increasing the driveline disconnect clutchapplication pressure. The DISG may be operated in speed feedback modewith a constant commanded speed (e.g. idle speed ˜700 RPM).Alternatively, the DISG speed may be chosen as a lower speed to reduceenergy consumption

At 4132, method 4100 adjusts DISG torque based in the present drivelinedisconnect clutch transfer function that is subject to adaptation afterthe driveline disconnect clutch application procedure is completed. Inparticular, the DISG torque is increased based on the amount of torqueestimated to be transferred from the DISG to the engine via thedriveline disconnect clutch according to the driveline disconnect clutchtransfer function. Method 4100 proceeds to 4134 after the DISG torque isadjusted.

At 4134, method 4100 compares the amount of torque transferred by thedriveline disconnect clutch to the commanded driveline disconnect clutchtransfer torque (e.g., the amount of driveline disconnect clutch torquerequested via the driveline disconnect clutch transfer function). In oneexample, the driveline disconnect clutch torque may be determined viathe following equations depending on the location of the drivelinetorque sensor:

If the torque sensor is at the torque converter impeller:

_(clutch) =I _(elec) _(—) _(machine) ·{dot over (N)} _(impeller) +T_(sensor) −T _(elec) _(—) _(machine)

If the torque sensor is at the torque converter turbine/input shaft:

_(clutch) =I _(elec) _(—) _(machine) ·{dot over (N)} _(impeller) +T_(sensor) −T _(elec) _(—) _(machine) −T _(turbine)

Where

$T_{turbine} = {\frac{N_{impeller}^{2} \cdot {{TR}\left( \frac{N_{turbine}}{N_{impeller}} \right)}}{{cpc}^{2}\left( \frac{N_{turbine}}{N_{impeller}} \right)} + T_{conv\_ clutch}}$

Where {circumflex over (T)}_(dutch) is the estimated drivelinedisconnect clutch torque, I_(elec) _(—) _(machine) is the inertia of theDISG, N_(impeller) is the torque converter impeller speed, T_(sensor) isthe torque measured via the torque sensor, T_(elec) _(—) _(machine) thetorque output n of the DISG, T_(turbine) is the torque of the torqueconverter turbine, cpc is the torque converter capacity factor,N_(turbine) is the torque converter turbine speed, and T_(conv) _(—)_(clutch) is the torque converter clutch torque.

During conditions where torque converter turbine speed is less thantorque converter impeller speed, the torque converter clutch is open,the driveline disconnect clutch is open (e.g., a desirable case isvehicle at rest with impeller spinning ˜700 rpm), adaptively correct thecapacity factor (cpc) of the torque converter based on motor torque andimpeller acceleration using the above equations. During conditions wherethe torque converter impeller is spinning, the driveline disconnectclutch is open, and engine restart is not commanded, drivelinedisconnect clutch torque are commanded sequentially higher. Based on thecurrent estimate of the driveline disconnect clutch stroke pressure ortouch-point (e.g., driveline disconnect clutch is commanded to a pointwhere the driveline disconnect clutch plates on the input and outputsides of the driveline disconnect clutch first contact when thedriveline disconnect clutch is transitioning from an open state to apartially closed state) of the driveline disconnect clutch, thedriveline disconnect clutch torque is compensated via DISG torque toreduce vehicle drivability impact. In one example, the DISG torque isincreased in proportion to an amount of the estimated drivelinedisconnect clutch torque based on the present clutch transfer function.

The driveline disconnect clutch torque estimate may be compared to themeasurement from the torque sensor with appropriate compensation fortorques and inertias between driveline disconnect clutch and torquesensor. The driveline disconnect clutch stroke pressure/touchpoint maybe adaptively adjusted. In one example, the driveline disconnect clutchtransfer function is adjusted via replacing a value in the drivelinedisconnect clutch transfer function with the estimated drivelinedisconnect clutch torque. Alternatively, the driveline disconnect clutchtransfer function may be adjusted based on an error between thedriveline disconnect clutch transfer function and the estimateddriveline disconnect clutch torque.

If the commanded driveline disconnect clutch torque is less than orgreater than the amount of torque transferred by the drivelinedisconnect clutch by a predetermined amount, the driveline disconnectclutch torque value in the driveline disconnect clutch transfer functionat the operating point is adjusted to the measured driveline disconnectclutch torque.

In this way, the driveline disconnect clutch transfer function can beadjusted to provide an improved estimate of the amount of torquetransferred by the driveline disconnect clutch. Method 4100 proceeds to4136 after the driveline disconnect clutch transfer function has beenassessed and/or adapted at the present operating conditions.

At 4136, method 4100 judges whether or not all the desired portions ofthe driveline disconnect clutch transfer function have been assessedand/or adjusted at all desired driveline disconnect clutch applicationpressures. If so, the answer is yes and method 4100 proceeds to 4138.Otherwise, the answer is no and method 4100 returns to 4130 where thedriveline disconnect clutch application pressure is increased and thedriveline disconnect clutch torque transfer function is evaluated at anew operating condition.

At 4138, method 4100 applies the revised driveline disconnect clutchtransfer function to scheduled driveline disconnect clutch pressure. Forexample, when an adjustment to driveline disconnect clutch pressure isrequested, the driveline disconnect clutch pressure is output based onthe revised driveline disconnect clutch transfer function at 4134.Method 4100 exits after the revised driveline disconnect clutchpressures are output.

At 4112, method 4100 increases the driveline disconnect clutchapplication pressure from a state where the driveline disconnect clutchis fully opened as described at 4130. The vehicle speed may be zero atthis time and the driveline disconnect clutch command may beincrementally increased to increase driveline disconnect clutchapplication pressure or force. Method 4100 proceeds to 4114 after thedriveline disconnect clutch application pressure is adjusted.

At 4114, method 4100 adjusts the DISG torque as described at 4132.Method 4100 proceeds to 4116 after the DISG torque is adjusted.

At 4116, method 4100 estimates the torque transferred by the drivelinedisconnect clutch based on speeds and accelerations of drivelinecomponents. In one example, the torque transferred by the drivelinedisconnect clutch may be estimated via the following equations:

I _(impeller) ·{dot over (N)} _(impeller) =T _(clutch) +T _(elec) _(—)_(mach) −T _(conv)

Where:

$T_{conv} = {\frac{N_{impeller}^{2}}{{cpc}^{2}\left( \frac{N_{turbine}}{N_{impeller}} \right)} + T_{conv\_ clutch}}$

Solving for driveline disconnect clutch torque:

_(clutch) =I _(impeller) ·{dot over (N)} _(impeller) −T _(elec) _(—)_(mach) +T _(conv)

Where I_(impeller) is torque converter impeller inertia, N_(impeller) istorque converter impeller speed, speed, T_(clutch) is torque of thedriveline disconnect clutch, T_(elec) _(—) _(machine) is the DISGtorque, T_(conv) is torque converter impeller torque, cpc is the intorque converter capacity factor, N_(turbine) is the torque converterturbine speed, and T_(conv) _(—) _(clutch) the torque converter clutchtorque.

During conditions where torque converter turbine speed is less thantorque converter impeller speed, torque converter bypass clutch is open,driveline disconnect clutch is open (e.g., a desirable case is vehicleat rest with impeller spinning ˜700 rpm), the capacity factor (cpc) ofthe torque converter, which is based on motor torque and impelleracceleration, is adaptively corrected via equations above. Duringconditions where the impeller is spinning, the driveline disconnectclutch is open, and engine restart is not commanded, sequentially higherdriveline disconnect clutch torques are commanded. The drivelinedisconnect clutch torque is compensated via DISG torque to reducedrivability impact. The driveline disconnect clutch torque is based onthe current estimate of the driveline disconnect clutch stroke pressureor the touchpoint of the driveline disconnect clutch.

For example, DISG torque is increased as the driveline disconnect clutchtorque is increased. In one example, the DISG torque is increased inproportion to the torque transferred via the driveline disconnectclutch. The driveline disconnect clutch torque estimate is compared to adriveline disconnect clutch torque calculated using the equations abovebased on other torques, speeds, and accelerations at 4118. Then thedriveline disconnect clutch stroke pressure/touchpoint of the drivelinedisconnect clutch is adaptively updated at 4118. Method 4100 proceeds to4118 after the amount of torque transferred by the driveline disconnectclutch is estimated.

At 4118, method 4100 compares the estimated torque transferred by thedriveline disconnect clutch with the driveline disconnect clutch torquefrom the present driveline disconnect clutch transfer function asdescribed at 4134. The comparison may be performed by subtracting theestimated driveline disconnect clutch torque from the desired drivelinedisconnect clutch torque to provide an error that is the basis foradapting the driveline disconnect clutch transfer function. When theerror is greater than a predetermined amount, the estimated drivelinedisconnect clutch torque replaces the value of driveline disconnectclutch in the driveline disconnect clutch transfer function or is thebasis for adjusting the driveline disconnect clutch transfer function.Method 4100 proceeds to 4120 after the estimated amount of torquetransferred by the driveline disconnect clutch is compared to thedriveline disconnect clutch torque from the driveline disconnect clutchtransfer function.

At 4120, method 4100 judges whether or not all the desired portions ofthe driveline disconnect clutch transfer function have been assessedand/or adjusted at all desired driveline disconnect clutch applicationpressures. If so, the answer is yes and method 4100 proceeds to 4122.Otherwise, the answer is no and method 4100 returns to 4112 where thedriveline disconnect clutch application pressure is increased and thedriveline disconnect clutch torque transfer function is evaluated at anew operating condition.

At 4122, method 4100 applies the revised driveline disconnect clutchtransfer function to scheduled driveline disconnect clutch pressure. Forexample, when an adjustment to driveline disconnect clutch pressure isrequested, the driveline disconnect clutch pressure is output based onthe revised driveline disconnect clutch transfer function at 4118.Method 4100 exits after the revised driveline disconnect clutchpressures are output.

In some examples, a driveline disconnect clutch may be used incombination with a dual clutch automatic transmission (DCT) (e.g., FIG.3). In these applications, the DISG may be used as a torque sensingdevice to measure the DCT launch clutch torque as a function of thecommanded DCT launch clutch torque at the low torque levels that thelaunch clutch operates at during an engine restart and launch. The gainand/or offset may then be updated in the DCT launch clutch torque tablesto match the actual input to output torque. One example of using theDISG to sense the DCT launch clutch torque includes: measuring the DCTlaunch clutch torque when the vehicle is stopped and the brakes areapplied, e.g. when the vehicle is at rest and the operator is applyingthe brake or the brake system is being commanded to delay the brakerelease. Such operation may be used to prevent the change in the DCTlaunch clutch torque from being either transmitted to the wheels oreffecting the vehicle acceleration.

In some examples, the driveline disconnect clutch may be open. An opendriveline disconnect clutch removes engine and/or dual mass flywheel(DMF) torque or compliance interactions that may impact the ability ofthe DISG to accurately sense the DCT launch clutch torque. The DISG maybe operated in speed feedback mode with a constant commanded speed, e.g.idle speed ˜700 RPM. The DISG speed may be chosen as a lower speed toreduce energy consumption. The DISG speed may be set to maintain thehydraulic pressure in the automatic transmission (AT) by using the DISGto spin the transmission hydraulic pump. Operating the DISG to maintaintransmission oil pressure applies to a DCT with hydraulic clutchesversus, a dry clutch DCT.

In some examples, the DCT launch clutch is fully open (e.g. with zerotorque capacity) when a DISG torque estimate is learned. The DISG torqueestimate is the basis for recording the open DCT launch clutch torque atthe commanded DISG speed. The DISG torque estimate is a function of DISGthree phase currents or of a commanded torque from an inner loop of theDISG speed feedback control. The DCT launch clutch is commanded tooperate over a desired torque range after the open DCT launch clutchtorque has been determined from the DISG torque estimate. The DCT launchclutch torques for each commanded torque in the desired torque range isdetermined from DISG torque determined at each commanded torque. A DCTlaunch clutch error torque is determined as a difference between theopen DCT launch clutch torque measure and the sensed torque from theDISG three phase current torque estimate or the commanded torque. TheDISG may be operated in speed feedback mode which includes an innertorque loop when determining the DCT launch clutch torque. The DCTtorque table or transfer function is updated to the according to theobserved DISG torque.

Further, variability in the actuation and estimation of torquetransferred via a TCC may be a noise factor that can contribute to poordrivability of the vehicle system. If the TCC torque is not actuatedcorrectly, due to errors in the commanded vs. the actual TCC torqueduring the engine restart process, the torque transferred to the wheelsmay be less than desired and the launch performance and drivability maybe degraded.

The DISG may be operated as a torque sensing device to measure torquetransferred via the TCC as a function of the commanded TCC torque duringengine starting. The low torque levels transmitted via the TCC duringengine starting and launch may be the basis for updating gain and/oroffset values in TCC torque tables so that table values match the actualinput to output torque.

One example of operating the DISG to sense the transferred TCC torqueincludes: measuring the TCC torque via the DISG when the vehicle isstopped and when the brakes are applied (e.g. when the vehicle is atrest and the operator is applying the brake). Another example includesestimating the transferred TCC torque via the DISG when automatictransmission clutches tie-up transmission output for hill hold purposes.Tying up the transmission reduces the possibility of transferred TCCtorque being transmitted to vehicle wheels.

The torque transferred via the TCC may be more accurately determinedwhen the driveline disconnect clutch is open since it removes engine,dual mass flywheel, or compliance interactions that may influence DISGtorque estimates. The DISG may be operated in speed feedback mode at alow constant commanded speed (e.g. idle speed ˜700 RPM) to reduce energyconsumption when the DISG is the basis for TCC torque transferestimates. The DISG speed may also be adjusted to maintain hydraulicpressure in the torque converter by rotating the transmission via theDISG.

The TCC transfer function, which describes the amount of torquetransferred by the TCC at selected application pressures or forces, maybe adapted based on DISG torque estimates. In one example, the TCC iscommanded fully open (e.g. with zero torque capacity) and torqueconverter output is estimated based on DISG current. The DISG current isconverted to a torque which is subtracted from torques determined atother TCC commands where the TCC is not commanded fully open. Thus, atorque offset is determined and stored to memory when the TCC iscommanded fully open. The TCC is then commanded in increments over adesired torque range while DISG torque is estimated from DISG current ateach commanded torque. A TCC transfer torque error amount is determinedfrom a difference between the TCC open loop torque command (e.g., theTCC transfer function) and TCC torque as determined from the DISG threephase current. The TCC transfer function may be updated based on the TCCtransfer torque error. In one example, a fraction of each TCC transfertorque error is added to the present value in the TCC transfer functionthat corresponds to the TCC transfer torque error.

In this way, the driveline disconnect clutch transfer function may berevised so that the driveline disconnect clutch may be applied moreaccurately. Further, the driveline disconnect clutch transfer functionmay be revised without taking actions that may be noticeable to thedriver.

Referring now to FIG. 43, an example sequence for updating or adapting adriveline disconnect clutch transfer function according to the methodsof FIGS. 41 and 42 is shown. The sequence of FIG. 43 may be provided bythe system of FIGS. 1-3.

The first plot from the top of FIG. 43 represents torque converterimpeller speed versus time. The Y axis represents torque converterimpeller speed and torque converter impeller speed increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure. Horizontal line 4302 represents a desired torqueconverter impeller speed.

The second plot from the top of FIG. 43 represents DISG torque versustime. The Y axis represents DISG torque and DISG torque increases in thedirection of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The third plot from the top of FIG. 43 represents the drivelinedisconnect clutch application force or pressure versus time. The Y axisrepresents driveline disconnect clutch application force or pressure andthe application force or pressure increases in the direction of the Yaxis arrow. The X axis represents time and time increases from the lefthand side of the figure to the right hand side of the figure.

Before time T₁₀₂, the torque converter impeller speed is at the desiredtorque converter impeller speed 4302 and the DISG torque is at a lowerlevel. The driveline disconnect clutch pressure is also at a lowervalue. If the DISG is in speed control, the magnitude of the change inDISG torque required to hold the desired impeller speed may be used asthe torque estimation mechanism similar to the way engine torque is usedin FIG. 42.

At time T₁₀₂, the driveline disconnect clutch pressure is increased inresponse to a request to increase torque transferred by the drivelinedisconnect clutch. The DISG torque is not increased since the drivelinedisconnect clutch transfer function indicates that torque is nottransferred by the driveline disconnect clutch at the present commandedvalue. The torque converter impeller speed remains at the desired torqueconverter impeller speed, or DISG torque is not required to change whilein closed loop speed control mode, and it indicates that the drivelinedisconnect clutch torque transfer function that estimates drivelinedisconnect clutch torque is correct. The driveline disconnect pressureis reduced after it is increased so that the next increase in disconnectclutch pressure may be initiated from a known condition.

At time T₁₀₃, the driveline disconnect clutch pressure is increased asecond time in response to a request to increase torque transferred bythe driveline disconnect clutch. The DISG torque is again not increasedsince the driveline disconnect clutch transfer function indicates thattorque is not transferred by the driveline disconnect clutch at thepresent commanded value. The torque converter impeller speed decreases,or DISG torque increases due to closed loop rpm control, to indicatethat the driveline disconnect clutch torque transfer function is underestimating the driveline disconnect clutch torque that is transferred.The driveline disconnect clutch transfer function error may bedetermined from a torque sensor at the disconnect clutch, DISG current,or from a model as described at 4116. The driveline disconnect clutchtransfer function is adjusted based on the error. In particular, in thisexample, the torque estimated for the output command is reduced by apredetermined amount. Alternatively, the output command for thedriveline disconnect clutch may be reduced by a predetermined amount.The driveline disconnect pressure is reduced after it is increased sothat the next increase in disconnect clutch pressure may be initiatedfrom a known condition.

At time T₁₀₄, the driveline disconnect clutch pressure is increased athird time in response to a request to increase torque transferred bythe driveline disconnect clutch. The DISG torque is increased since thedriveline disconnect clutch transfer function indicates that torque istransferred by the driveline disconnect clutch at the present commandedvalue. The torque converter impeller speed increases, or DISG torque isadjusted via the closed loop rpm control to not increase as much as thedisconnect clutch transfer function would indicate, to indicate that thedriveline disconnect clutch torque transfer function is over estimatingthe driveline disconnect clutch torque that is transferred. Thedriveline disconnect clutch transfer function error may be determinedand the driveline disconnect clutch transfer function is adjusted basedon the error. In particular, in this example, the torque estimated forthe output command is increased by a predetermined amount.Alternatively, the output command for the driveline disconnect clutchmay be increased by a predetermined amount. The driveline disconnectpressure is reduced after it is increased so that the next increase indisconnect clutch pressure may be initiated from a known condition.

At time T₁₀₅, the driveline disconnect clutch pressure is increased afourth time in response to a request to increase torque transferred bythe driveline disconnect clutch. The DISG torque is increased since thedriveline disconnect clutch transfer function indicates that torque istransferred by the driveline disconnect clutch at the present commandedvalue. The torque converter impeller speed stays constant to indicatethat the driveline disconnect clutch torque transfer function iscorrectly estimating the driveline disconnect clutch torque that istransferred. The driveline disconnect clutch transfer function is notadjusted since there is less than a threshold amount of error in theestimate of driveline disconnect clutch torque transfer. The drivelinedisconnect pressure is reduced after it is increased so that the nextincrease in disconnect clutch pressure may be initiated from a knowncondition.

In this way, a transfer function that describes torque transferred by adriveline disconnect clutch may be adapted. Each driveline disconnectclutch application pressure in the transfer function may be adapted inthis way so that the entire transfer function may be revised as thevehicle ages.

Referring now to FIG. 44, an example sequence for updating or adapting adriveline disconnect clutch transfer function according to the method ofFIG. 42 is shown. The sequence of clutch torques shown in FIG. 43 may beapplied to the sequence of FIG. 42. The sequence of FIG. 44 may beprovided by the system of FIGS. 1-3.

The first plot from the top of FIG. 44 represents engine speed versustime. The Y axis represents engine speed and engine speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure. Horizontal line 4402 represents a desired engine speed.

The second plot from the top of FIG. 44 represents engine torque versustime. The Y axis represents engine torque and engine torque increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left hand side of the figure to the right hand sideof the figure.

The third plot from the top of FIG. 44 represents the drivelinedisconnect clutch application force or pressure versus time. The Y axisrepresents driveline disconnect clutch application force or pressure andthe application force or pressure increases in the direction of the Yaxis arrow. The X axis represents time and time increases from the lefthand side of the figure to the right hand side of the figure.

Before time T₁₀₆, the engine speed is at the desired engine speed 4402and the engine torque is at a lower level. The driveline disconnectclutch pressure is also at a lower value and commanding the drivelinedisconnect clutch to an open position. The engine is in a speed controlmode and engine torque is determined from engine speed and engine load(e.g., present engine air mass divided by theoretical air mass theengine is capable of inducting whether naturally aspirated orsupercharged). The DISG and torque converter speed (not shown) areadjusted to a speed that is different than the desired engine speed.

At time T₁₀₆, the driveline disconnect clutch pressure is increased inresponse to a request to increase torque transferred by the drivelinedisconnect clutch. The DISG speed (not shown) remains constant and thedesired engine speed remains constant as the driveline disconnect clutchapplication force is increased. The engine torque initially remains at aconstant level as the driveline disconnect clutch is gradually closed.

At time T₁₀₇, the driveline disconnect clutch pressure continues toincrease and the engine speed begins to decelerate to a speed less thanthe desired engine speed. The engine speed control loop increases enginetorque (e.g., via opening the engine throttle) in response thedifference between desired engine speed and actual engine speed. Theestimated driveline disconnect clutch torque is the difference betweenthe engine torque before time T₁₀₆ and the engine torque at time afterT₁₀₆ when the driveline disconnect clutch application force is increased(e.g., at time shortly after time T₁₀₇). The driveline disconnect clutchtransfer function which outputs a driveline disconnect clutchapplication force or pressure in response to a desired drivelinedisconnect clutch torque may be adjusted based on the estimateddriveline torque.

In this example, the driveline disconnect clutch transfer functionentries that deviate from the estimated driveline disconnect clutchtorque values determined at the commanded driveline disconnect clutchpressures may be updated to the estimated driveline disconnect clutchtorque or by a fraction of the error if they vary from the estimateddriveline disconnect clutch torque by more than a threshold amount oftorque. The driveline disconnect clutch transfer function may be updatedas the adaption process occurs or after the sequence is complete. Itshould also be noted that the engine speed may increase instead ofdecrease at time T₁₀₇ when torque converter impeller speed is greaterthan engine speed. In this example, torque converter impeller speed isadjusted to a speed greater than engine speed so that engine speedincreases at time T₁₀₇ when the driveline disconnect clutch is closed.

At time T₁₀₈, the driveline disconnect clutch pressure is decreased inresponse to a request to decrease torque transferred by the drivelinedisconnect clutch. The actual engine speed is greater than the desiredengine speed after the driveline disconnect clutch application pressureis reduced. The driveline disconnect clutch transfer function may beupdated when the estimated driveline disconnect clutch torque variesfrom the entry in the driveline disconnect clutch transfer functionvaries from the estimated driveline disconnect clutch torque.

In this way, a transfer function that describes torque transferred by adriveline disconnect clutch may be adapted. Each driveline disconnectclutch application pressure in the transfer function may be adapted inthis way so that the entire transfer function may be revised as thevehicle ages.

The methods and systems of FIGS. 1-3 and 41-44 also provide a drivelinedisconnect clutch adaptation method, comprising: adjusting applicationforce of a driveline disconnect clutch in a vehicle driveline inresponse to a torque sensor while an engine in the vehicle driveline isnot combusting air and fuel. In this way, a driveline disconnect clutchtransfer function may be adapted to improve vehicle drivability. Themethod further comprises adapting a transfer function of the drivelinedisconnect clutch in response to the torque sensor. The method includeswhere a transfer function of the driveline disconnect clutch is adaptedin response to a response of driveline components.

In some examples, the method includes where adjusting application of thedriveline disconnect clutch is based on increasing driveline disconnectclutch application pressure from a condition where the drivelinedisconnect clutch is open. The method includes where a drivelineintegrated starter/generator is rotating during adjusting application ofthe driveline disconnect clutch. The method includes where atransmission lock-up clutch is open during adjusting application of thedriveline disconnect clutch.

The methods and systems of FIGS. 1-3 and 41-44 also provide for adriveline disconnect clutch adaptation method, comprising: rotating atorque converter impeller at a speed less than a speed where greaterthan a threshold percentage of torque at the torque converter impelleris transferred to a torque converter turbine, the torque converterimpeller in a vehicle driveline; and adjusting application force of adriveline disconnect clutch in the vehicle driveline in response to atorque sensor while an engine in the vehicle driveline is not combustingair and fuel. The driveline disconnect clutch adaptation method includeswhere the speed is less than 700 RPM.

In one example, the driveline disconnect clutch adaptation methodincludes where the application force is adjusted via adapting adriveline disconnect clutch transfer function. The driveline disconnectclutch adaptation method further comprises increasing a drivelinedisconnect clutch command and adjusting the driveline disconnect clutchtransfer function based on output of the torque sensor. The drivelinedisconnect clutch adaptation method further comprises commanding openingof a torque converter clutch. The driveline disconnect clutch adaptationmethod includes where the torque converter impeller is rotated via adriveline integrated starter/generator. The driveline disconnect clutchadaptation method includes where the driveline integratedstarter/generator rotates at a speed that generates a thresholdtransmission oil pressure that holds a transmission clutch in an appliedstate. The driveline disconnect clutch adaptation method includes wherethe torque converter impeller rotates at a speed greater than a speed ofthe torque converter turbine.

The methods and systems of FIGS. 1-3 and 41-44 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller including executableinstructions stored in non-transitory memory to adjust an estimate oftorque transferred through the driveline disconnect clutch in responseto a torque sensor output. The vehicle system includes where the engineis not combusting air and fuel.

In some examples, the vehicle system further comprises rotating the DISGat a speed below which a threshold percent of DISG torque is transferredto the transmission. The vehicle system further comprises a torqueconverter including a torque converter clutch and additionalinstructions to open the torque converter clutch while adjusting theestimate of torque transferred through the driveline disconnect clutch.The vehicle system further comprises additional instructions to rotatean impeller of the torque converter at a higher speed than a turbine ofthe torque converter. The vehicle system further comprises additionalinstructions to increase a closing force applied to the drivelinedisconnect clutch.

The methods and systems of FIGS. 1-3 and 41-44 also provide for adriveline disconnect clutch adaptation method, comprising: rotating atorque converter impeller at a first speed; operating an engine in aspeed control mode and rotating the engine at a second speed differentfrom the first speed; and adjusting a driveline disconnect clutchtransfer function in response to a torque estimate based on engineoperating conditions. The method includes where the torque converterimpeller is rotated via a driveline integrated starter/generator.

In some examples, the method includes where the second speed is greaterthan the first speed. The method includes where the second speed is lessthan the first speed. The method includes where the engine operatingconditions are engine speed and engine load. The method furthercomprises commanding an increase in application force of a drivelinedisconnect clutch. The method further comprises adjusting engine torqueto maintain engine speed at the second speed while commanding theincrease in application force of the driveline disconnect clutch.

The methods and systems of FIGS. 1-3 and 41-44 also provide for adriveline disconnect clutch adaptation method, comprising: rotating atorque converter impeller at a first speed; operating an engine in aspeed control mode and rotating the engine at a second speed differentfrom the first speed; storing an engine torque output value in responseto an open driveline disconnect clutch; incrementally closing thedriveline disconnect clutch; and adjusting a driveline disconnect clutchtransfer function in response to a difference between a torque estimatebased on engine operating conditions and a torque estimate based on thedriveline disconnect clutch transfer function.

In one example, the driveline disconnect clutch adaptation methodincludes where the first speed is less than 700 RPM. The drivelinedisconnect clutch adaptation method includes where the engine operatingconditions are engine speed and load. The driveline disconnect clutchadaptation method includes where the torque estimate based on engineoperating conditions is an engine torque minus engine torque storedduring the open driveline disconnect clutch. The driveline disconnectclutch adaptation method also includes where engine speed is adjustedvia adjusting engine torque during the speed control mode. The drivelinedisconnect clutch adaptation method includes where the torque converterimpeller is rotated via a driveline integrated starter/generator. Thedriveline disconnect clutch adaptation method includes where thedriveline integrated starter/generator rotates at a speed that generatesa threshold transmission oil pressure that holds a transmission clutchin an applied state. The driveline disconnect clutch adaptation methodincludes where the torque converter impeller rotates at a speed greaterthan a speed of the torque converter turbine.

The methods and systems of FIGS. 1-3 and 41-44 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller including executableinstructions stored in non-transitory memory to adjust an estimate oftorque transferred through the driveline disconnect clutch in responseto an engine torque estimate. The vehicle system includes where theengine torque estimate is based on engine speed and load.

In some examples, the vehicle system further comprises additionalinstructions for rotating the DISG and the engine, at a speed belowwhich a threshold percent of DISG torque is transferred to thetransmission. The vehicle system further comprises additionalinstructions for rotating the DISG at a speed that is less than a speedof engine rotation. The vehicle system further comprises additionalinstructions to perform closed loop engine speed control via adjustingengine torque while estimating the engine torque.

The methods and systems of FIGS. 1-3 and 41-44 also provide for adriveline disconnect clutch adaptation method, comprising: adjustingapplication force of a driveline disconnect clutch in a vehicledriveline in response to a torque sensor while an engine in the vehicledriveline is not combusting air and fuel. The method further comprisesadapting a transfer function of the driveline disconnect clutch inresponse to the torque sensor. The method includes where a transferfunction of the driveline disconnect clutch is adapted in response to aresponse of driveline components. The method includes where adjustingapplication of the driveline disconnect clutch is based on increasingdriveline disconnect clutch application pressure from a condition wherethe driveline disconnect clutch is open. The method includes where adriveline integrated starter/generator is rotating during adjustingapplication of the driveline disconnect clutch. The method includeswhere a transmission lock-up clutch is open during adjusting applicationof the driveline disconnect clutch.

The methods and systems of FIGS. 1-3 and 41-44 also provide for adriveline disconnect clutch adaptation method, comprising: rotating atorque converter impeller at a speed less than a speed where greaterthan a threshold percentage of torque at the torque converter impelleris transferred to a torque converter turbine, the torque converterimpeller in a vehicle driveline; and adjusting application force of adriveline disconnect clutch in the vehicle driveline in response to atorque sensor while an engine in the vehicle driveline is not combustingair and fuel. The driveline disconnect clutch adaptation method includeswhere the speed is less than 700 RPM.

In some examples, the driveline disconnect clutch adaptation methodincludes where the application force is adjusted via adapting adriveline disconnect clutch transfer function. The driveline disconnectclutch adaptation method further comprises increasing a drivelinedisconnect clutch command and adjusting the driveline disconnect clutchtransfer function based on output of the torque sensor. The drivelinedisconnect clutch adaptation method further comprises commanding openingof a torque converter clutch. The driveline disconnect clutch adaptationmethod includes where the torque converter impeller is rotated via adriveline integrated starter/generator. The driveline disconnect clutchadaptation method includes where the driveline integratedstarter/generator rotates at a speed that generates a thresholdtransmission oil pressure that holds a transmission clutch in an appliedstate. The driveline disconnect clutch adaptation method includes wherethe torque converter impeller rotates at a speed greater than a speed ofthe torque converter turbine.

The methods and systems of FIGS. 1-3 and 41-44 also provide for avehicle system, comprising: an engine; a dual mass flywheel including afirst side mechanically coupled to the engine; a driveline disconnectclutch mechanically including a first side coupled to a second side ofthe dual mass flywheel; a driveline integrated starter/generator (DISG)including a first side coupled to a second side of the drivelinedisconnect clutch; a transmission selectively coupled to the engine viathe driveline disconnect clutch; and a controller including executableinstructions stored in non-transitory memory to adjust an estimate oftorque transferred through the driveline disconnect clutch in responseto a torque sensor output.

In one example, the vehicle system includes where the engine is notcombusting air and fuel. The vehicle system further comprises rotatingthe DISG at a speed below which a threshold percent of DISG torque istransferred to the transmission. The vehicle system further comprises atorque converter including a torque converter clutch and additionalinstructions to open the torque converter clutch while adjusting theestimate of torque transferred through the driveline disconnect clutch.The vehicle system further comprises additional instructions to rotatean impeller of the torque converter at a higher speed than a turbine ofthe torque converter. The vehicle system further comprises additionalinstructions to increase a closing force applied to the drivelinedisconnect clutch.

The methods and systems described above may infer torque at differentlocations of a torque converter. FIGS. 45-48 describe one example ofdetermining torque at the torque converter impeller and turbine.

Referring now to FIG. 45, a function that describes a torque converter Kfactor is shown. The torque converter K factor is related to the speedratio of the torque converter impeller and turbine. The K factor or FIG.45 may be expressed as:

$K = {{fn}\left( \frac{N_{turbine}}{N_{impeller}} \right)}$

where K is the torque converter K factor, N_(turbine) is torqueconverter turbine speed, and N_(impeller) is torque converter impellerspeed, an fn is a function describing the K factor. Then, torque at thetorque converter impeller may be described by:

$T_{imp} = {1.558 \cdot \frac{N_{impeller}^{2}}{K^{2}}}$

where T_(imp) is torque converter impeller torque, and where 1.558 is aconversion factor from ft-lbf to N-m. The above relationships hold forspeed ratios<1.

Referring now to FIG. 46, a function that describes a torque convertercapacity factor as a function of a ratio of torque converter impellerspeed to torque converter turbine speed is shown. The capacity factor isrelated to the K factor according to the equation:

${Capacity\_ Factor} = \frac{1}{K^{2}}$

where Capacity_Factor is the torque converter capacity factor and whereK is the torque converter K factor described above. The functiondescribed in FIG. 46 may be used in conjunction with the functionsdescribed in FIGS. 47 and 48 to model behavior of a torque converter.The individual entries that form the curve shown in FIG. 46 may beempirically determined and stored in controller memory.

Referring now to FIG. 47, a function that describes a torque convertertorque ratio (TR) as a function of a ratio of torque converter impellerspeed to torque converter turbine speed is shown. The function describedin FIG. 47 may be used in conjunction with the functions described inFIGS. 46 and 48 to model behavior of a torque converter. The individualentries that form the curve shown in FIG. 47 may be empiricallydetermined and stored in controller memory. The function shown in FIG.47 includes a Y axis that represents a torque converter torque ratio.The X axis represents the torque converter impeller to turbine speedratio. It may be observed that there is an inverse relationship betweentorque converter torque ratio and torque converter impeller to turbinespeed ratio. The TR may be described as:

${TR} = {{fn}\left( \frac{N_{turbine}}{N_{impeller}} \right)}$

where TR is the torque converter torque ratio, fn is a functiondescribing the torque ratio, N_(turbine) is torque converter turbinespeed, and N_(impeller) is torque converter impeller speed. The torqueconverter torque ratio is related to the torque converter impeller speedvia the equation:

T_(turbine) = T_(impeller) ⋅ TR or${Tturbine} = {1.558 \cdot \frac{N_{impeller}^{2}}{K^{2}} \cdot {TR}}$

Referring now to FIG. 48, a function that describes a torque convertercapacity factor of FIG. 46 multiplied by the torque converter torqueratio of FIG. 47 as a function of a ratio of torque converter impellerspeed to torque converter turbine speed is shown.

The function described in FIG. 48 may be used in conjunction with thefunctions described in FIGS. 46 and 47 to model behavior of a torqueconverter. The individual entries that form the curve shown in FIG. 48may be empirically determined and stored in controller memory. Thefunction shown in FIG. 48 includes a Y axis that represents a torqueconverter capacity factor multiplied by the torque converter torqueratio. The Y axis represents the torque converter impeller to turbinespeed ratio.

In one example, the function in FIG. 46 is indexed by the ratio oftorque converter impeller speed to torque converter turbine speed andits output is multiplied by the torque converter impeller speed squaredto provide an estimate of torque converter impeller torque. The functionin FIG. 47 is indexed by the ratio of torque converter impeller speed totorque converter turbine speed and its output is multiplied by thefunction in FIG. 48 to provide an estimate of torque converter turbinetorque. The torque across the torque converter is the difference betweenthe torque converter impeller torque and the torque converter turbinetorque. Of course, inverse operations to determine torque converterimpeller speed and torque converter turbine speed may also be performed.

Thus, operation of a torque converter may be estimated according to amodel comprising the functions described in FIGS. 45-48. In particular,the torque converter may provide an estimate of torque converterimpeller torque or torque converter turbine torque as an estimate ofDISG torque or wheel torque since the torque converter is mechanicallycoupled to the DISG and the transmission.

As will be appreciated by one of ordinary skill in the art, methodsdescribed in FIGS. 4-44 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,13, 14, 15, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

1. A method of starting an engine, comprising: during a first condition, starting an engine with a first electrical machine while a driveline disconnect clutch is closed; and during a second condition, starting the engine with a second electrical machine while the driveline disconnect clutch is open.
 2. The method of claim 1, where the second electrical machine has a lower power output capacity than the first electrical machine.
 3. The method of claim 2, where the first electrical machine is a driveline integrated starter/generator (DISG), and where the driveline disconnect clutch has a first side mechanically coupled to a dual mass flywheel and a second side mechanically coupled to the DISG.
 4. The method of claim 1, where the first condition is a desired driveline torque that is less than a driveline torque during the second condition.
 5. The method of claim 1, where the driveline disconnect clutch is opened in response to a desired driveline torque.
 6. The method of claim 1, where the driveline disconnect clutch is closed when a sum of a desired driveline torque and an engine starting torque are greater than a threshold amount of torque.
 7. The method of claim 1, where the first electrical machine is positioned downstream of an engine and provides torque through a torque converter that rotates vehicle wheels, and where the second electrical machine is positioned at the engine and does not provide torque through the torque converter to rotate vehicle wheels above an engine cranking speed that is lower than engine idle speed.
 8. A method of starting an engine, comprising: starting an engine via a first electrical machine when a desired torque demand is less than a first threshold amount; starting the engine via the second electrical machine when the desired torque demand is greater than the first threshold amount; and supplying torque sufficient to rotate vehicle wheels solely via the first electrical machine during selected operating conditions.
 9. The method of claim 8, where the first electric machine is a driveline integrated starter/generator (DISG) and where the DISG is located in the hybrid vehicle driveline at a location between a driveline disconnect clutch and a transmission.
 10. The method of claim 9, where the DISG provides torque to start rotation of the stopped engine via at least partially closing the driveline disconnect clutch.
 11. The method of claim 8, further comprising decoupling the second electrical machine from the engine when engine speed reaches a threshold speed.
 12. The method of claim 11, where the second electrical machine includes a pinion shaft and a pinion gear.
 13. The method of claim 8, where the first threshold amount varies with battery state of charge.
 14. The method of claim 8, where the first threshold amount varies with speed of the first electrical machine.
 15. A hybrid vehicle system, comprising: an engine; a starter selectively engaged to the engine and including a pinion gear; a dual mass flywheel (DMF) including a first side mechanically coupled to the engine; a driveline disconnect clutch mechanically including a first side coupled to a second side of the dual mass flywheel; a driveline integrated starter/generator (DISG) including a first side coupled to a second side of the driveline disconnect clutch; and a controller including non-transitory instructions executable to start the engine via the starter during a first start and via the DISG during a second start.
 16. The hybrid vehicle system of claim 15, further comprising additional instructions to start the engine via the starter during conditions of a desired torque greater than a threshold.
 17. The hybrid vehicle system of claim 15, where the engine is started by rotating the engine via the DISG, and further comprising additional instructions to decouple the DISG from the engine after a predetermined number of combustion events.
 18. The hybrid vehicle system of claim 17, further comprising additional instructions to couple the engine to the DISG after engine speed reaches DISG speed.
 19. The hybrid vehicle system of claim 15, where available power output from the starter is lower than available power output from the DISG.
 20. The hybrid vehicle system of claim 15, further comprising additional instructions to automatically stop the engine, and where the engine is started via the DISG based on an available amount of DISG output torque. 